diff --git a/exercises/B-hello-world/exercise.js b/exercises/B-hello-world/exercise.js
index b179ee953..e26655452 100644
--- a/exercises/B-hello-world/exercise.js
+++ b/exercises/B-hello-world/exercise.js
@@ -1 +1,3 @@
-console.log("Hello world");
+console.log("Hello world." + " " + "I just started learning JavaScript!");
+// console.log(" " + "I just started learning JavaScript!");
+console.log(7);
diff --git a/exercises/C-variables/exercise.js b/exercises/C-variables/exercise.js
index a6bbb9786..7beea3261 100644
--- a/exercises/C-variables/exercise.js
+++ b/exercises/C-variables/exercise.js
@@ -1,3 +1,5 @@
 // Start by creating a variable `greeting`
-
+var greeting = "Hello world";
+console.log(greeting);
+console.log(greeting);
 console.log(greeting);
diff --git a/exercises/D-strings/exercise.js b/exercises/D-strings/exercise.js
index 2cffa6a81..9a78510f5 100644
--- a/exercises/D-strings/exercise.js
+++ b/exercises/D-strings/exercise.js
@@ -1,3 +1,5 @@
 // Start by creating a variable `message`
-
+var message = "This is a string";
+var messageType = typeof message;
 console.log(message);
+console.log(messageType);
diff --git a/exercises/E-strings-concatenation/exercise.js b/exercises/E-strings-concatenation/exercise.js
index 2cffa6a81..b2d7c80a3 100644
--- a/exercises/E-strings-concatenation/exercise.js
+++ b/exercises/E-strings-concatenation/exercise.js
@@ -1,3 +1,5 @@
 // Start by creating a variable `message`
-
-console.log(message);
+var greetingStart = "Hello, my name is ";
+var name = "Mohammad";
+var greeting = greetingStart + name;
+console.log(greeting);
diff --git a/exercises/F-strings-methods/exercise.js b/exercises/F-strings-methods/exercise.js
index 2cffa6a81..3f54894a0 100644
--- a/exercises/F-strings-methods/exercise.js
+++ b/exercises/F-strings-methods/exercise.js
@@ -1,3 +1,11 @@
 // Start by creating a variable `message`
+var name = "Mohammad";
+var nameLength = name.length;
 
-console.log(message);
+console.log(nameLength);
+
+var name = "Mohammad";
+var nameLowerCase = name.toLowerCase();
+
+console.log(nameLowerCase);
+console.log(nameLowerCase.trim());
diff --git a/exercises/F-strings-methods/exercise2.js b/exercises/F-strings-methods/exercise2.js
index b4b46943d..f8f1c2b6b 100644
--- a/exercises/F-strings-methods/exercise2.js
+++ b/exercises/F-strings-methods/exercise2.js
@@ -1,3 +1,3 @@
 const name = " Daniel  ";
 
-console.log(message);
+console.log(name.trim());
diff --git a/exercises/G-numbers/exercise.js b/exercises/G-numbers/exercise.js
index 49e7bc00b..2dfb5f55d 100644
--- a/exercises/G-numbers/exercise.js
+++ b/exercises/G-numbers/exercise.js
@@ -1 +1,13 @@
 // Start by creating a variables `numberOfStudents` and `numberOfMentors`
+var sum = 10 + 2; // 12
+var product = 10 * 2; // 20
+var quotient = 10 / 2; // 5
+var difference = 10 - 2; // 8
+
+const numberOfStudents = 23;
+const numberOfMentors = 3;
+const total = numberOfMentors + numberOfStudents;
+console.log("number of students: " + numberOfStudents);
+console.log("number of mentor: " + numberOfMentors);
+
+console.log("Total number of students and mentors: " + total);
diff --git a/exercises/I-floats/exercise.js b/exercises/I-floats/exercise.js
index a5bbcd852..6e8072312 100644
--- a/exercises/I-floats/exercise.js
+++ b/exercises/I-floats/exercise.js
@@ -1,2 +1,13 @@
 var numberOfStudents = 15;
 var numberOfMentors = 8;
+var preciseAge = 30.612437;
+var roughAge = Math.round(preciseAge); // 30
+let percentageOfStudents = Math.round(
+  (numberOfStudents * 100) / (numberOfMentors + numberOfStudents)
+);
+let percentageOfMentors = Math.round(
+  (numberOfMentors * 100) / (numberOfMentors + numberOfStudents)
+);
+
+console.log("Percentage mentors: " + percentageOfMentors + "%");
+console.log("Percentage students: " + percentageOfStudents + "%");
diff --git a/exercises/J-functions/exercise.js b/exercises/J-functions/exercise.js
index 0ae5850e5..98fda6220 100644
--- a/exercises/J-functions/exercise.js
+++ b/exercises/J-functions/exercise.js
@@ -1,7 +1,11 @@
 function halve(number) {
   // complete the function here
+  return number * 0.5;
 }
 
 var result = halve(12);
+// var result = halve(33);
+// var result = halve(7);
+// var result = halve(80);
 
 console.log(result);
diff --git a/exercises/J-functions/exercise2.js b/exercises/J-functions/exercise2.js
index 82ef5e780..468d45596 100644
--- a/exercises/J-functions/exercise2.js
+++ b/exercises/J-functions/exercise2.js
@@ -1,5 +1,6 @@
 function triple(number) {
   // complete function here
+  return number * 3;
 }
 
 var result = triple(12);
diff --git a/exercises/K-functions-parameters/exercise.js b/exercises/K-functions-parameters/exercise.js
index 8d5db5e69..89b92f9db 100644
--- a/exercises/K-functions-parameters/exercise.js
+++ b/exercises/K-functions-parameters/exercise.js
@@ -1,8 +1,8 @@
 // Complete the function so that it takes input parameters
-function multiply() {
+function multiply(a, b) {
   // Calculate the result of the function and return it
 }
-
+return a + b;
 // Assign the result of calling the function the variable `result`
 var result = multiply(3, 4);
 
diff --git a/exercises/K-functions-parameters/exercise2.js b/exercises/K-functions-parameters/exercise2.js
index db7a8904b..e7c787d04 100644
--- a/exercises/K-functions-parameters/exercise2.js
+++ b/exercises/K-functions-parameters/exercise2.js
@@ -1,5 +1,7 @@
 // Declare your function first
-
+function divide(a, b) {
+  return a / b;
+}
 var result = divide(3, 4);
 
 console.log(result);
diff --git a/exercises/K-functions-parameters/exercise3.js b/exercises/K-functions-parameters/exercise3.js
index 537e9f4ec..33884e789 100644
--- a/exercises/K-functions-parameters/exercise3.js
+++ b/exercises/K-functions-parameters/exercise3.js
@@ -1,5 +1,8 @@
 // Write your function here
 
+function createGreeting(name) {
+  return "Hello. my name is " + name;
+}
 var greeting = createGreeting("Daniel");
 
 console.log(greeting);
diff --git a/exercises/K-functions-parameters/exercise4.js b/exercises/K-functions-parameters/exercise4.js
index 7ab44589e..6d6bfb1c4 100644
--- a/exercises/K-functions-parameters/exercise4.js
+++ b/exercises/K-functions-parameters/exercise4.js
@@ -1,5 +1,7 @@
 // Declare your function first
-
+function add(a, b) {
+  return a + b;
+}
 // Call the function and assign to a variable `sum`
-
+let sum = add(13, 124);
 console.log(sum);
diff --git a/exercises/K-functions-parameters/exercise5.js b/exercises/K-functions-parameters/exercise5.js
index 7c5bcd605..42efb7c66 100644
--- a/exercises/K-functions-parameters/exercise5.js
+++ b/exercises/K-functions-parameters/exercise5.js
@@ -1,5 +1,7 @@
 // Declare your function here
-
-const greeting = createLongGreeting("Daniel", 30);
+function createLongGreeting(name, age) {
+  return `Hello, my name is ${name} and I'm ${age} years old`;
+}
+const greeting = createLongGreeting("Shayan", 23);
 
 console.log(greeting);
diff --git a/exercises/L-functions-nested/exercise.js b/exercises/L-functions-nested/exercise.js
index a5d377442..b1463b30e 100644
--- a/exercises/L-functions-nested/exercise.js
+++ b/exercises/L-functions-nested/exercise.js
@@ -3,3 +3,20 @@ var mentor2 = "Irina";
 var mentor3 = "Mimi";
 var mentor4 = "Rob";
 var mentor5 = "Yohannes";
+function nameUppercase(name) {
+  return name.toUpperCase();
+}
+
+function greetingMentors(name) {
+  return `HELLO lovely ${nameUppercase(name)}! welcome to my js test!`;
+}
+
+function greetingMentorsShouty(name) {
+  console.log(greetingMentors(name));
+}
+
+greetingMentorsShouty(mentor1);
+greetingMentorsShouty(mentor2);
+greetingMentorsShouty(mentor3);
+greetingMentorsShouty(mentor4);
+greetingMentorsShouty(mentor5);
diff --git a/mandatory/1-syntax-errors.js b/mandatory/1-syntax-errors.js
index a10cc9ac2..27931c68b 100644
--- a/mandatory/1-syntax-errors.js
+++ b/mandatory/1-syntax-errors.js
@@ -1,16 +1,16 @@
 // There are syntax errors in this code - can you fix it to pass the tests?
 
-function addNumbers(a b c) {
+function addNumbers(a, b, c) {
   return a + b + c;
 }
 
-function introduceMe(name, age)
-  return "Hello, my name is " + name "and I am " age + "years old";
-
+function introduceMe(name, age) {
+  return "Hello, my name is " + name + " and I am " + age + " years old";
+}
 function getTotal(a, b) {
-  total = a ++ b;
+  let total = a + b;
 
-  return "The total is total";
+  return "The total is " + total;
 }
 
 /* 
diff --git a/mandatory/2-logic-error.js b/mandatory/2-logic-error.js
index 9cca7603b..37c4ebc15 100644
--- a/mandatory/2-logic-error.js
+++ b/mandatory/2-logic-error.js
@@ -1,16 +1,15 @@
 // The syntax for this function is valid but it has an error, find it and fix it.
 
 function trimWord(word) {
-  return wordtrim();
+  return word.trim();
 }
 
 function getStringLength(word) {
-  return "word".length();
+  return word.length;
 }
 
 function multiply(a, b, c) {
-  a * b * c;
-  return;
+  return a * b * c;
 }
 
 /* 
diff --git a/mandatory/3-function-output.js b/mandatory/3-function-output.js
index 5a953ba60..be1172578 100644
--- a/mandatory/3-function-output.js
+++ b/mandatory/3-function-output.js
@@ -3,14 +3,19 @@ function getRandomNumber() {
   return Math.random() * 10;
 }
 
+/* The Math.random() function returns a floating-point, pseudo-random number that's greater than or equal to 0 and less than 1, with approximately uniform distribution over that range — which you can then scale to your desired range. The implementation selects the initial seed to the random number generation algorithm; it cannot be chosen or reset by the user. */
 // Add comments to explain what this function does. You're meant to use Google!
 function combine2Words(word1, word2) {
   return word1.concat(word2);
 }
 
+/* The concat() method is used to merge two or more arrays. This method does not change the existing arrays, but instead returns a new array. */
 function concatenate(firstWord, secondWord, thirdWord) {
   // Write the body of this function to concatenate three words together.
   // Look at the test case below to understand what this function is expected to return.
+
+  // return firstWord.concat(secondWord).concat(thirdWord);
+  return `${firstWord} ${secondWord} ${thirdWord}`;
 }
 
 /* 
diff --git a/mandatory/4-tax.js b/mandatory/4-tax.js
index ba77c7ae2..3a8e96871 100644
--- a/mandatory/4-tax.js
+++ b/mandatory/4-tax.js
@@ -5,7 +5,10 @@
   Sales tax is 20% of the price of the product.
 */
 
-function calculateSalesTax() {}
+function calculateSalesTax(price) {
+  let tax = price + (price * 20) / 100;
+  return tax;
+}
 
 /*
   CURRENCY FORMATTING
@@ -17,7 +20,9 @@ function calculateSalesTax() {}
   Remember that the prices must include the sales tax (hint: you already wrote a function for this!)
 */
 
-function addTaxAndFormatCurrency() {}
+function addTaxAndFormatCurrency(price) {
+  return `£${(price + (price * 20) / 100).toFixed(2)}`;
+}
 
 /* 
 ===================================================