diff --git a/mandatory/1-syntax-errors.js b/mandatory/1-syntax-errors.js
index d9e004465..bc5d3c429 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 "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;
+  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 9eb8c8cd7..6492e81f0 100644
--- a/mandatory/2-logic-error.js
+++ b/mandatory/2-logic-error.js
@@ -1,16 +1,17 @@
 // The syntax for these functions is valid but there are some errors, find them and fix them
 
 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..b02663ea4 100644
--- a/mandatory/3-function-output.js
+++ b/mandatory/3-function-output.js
@@ -2,15 +2,20 @@
 function getRandomNumber() {
   return Math.random() * 10;
 }
+//Math.random() returns a random number between 0 (inclusive),  and 1 (exclusive)
+
 
 // Add comments to explain what this function does. You're meant to use Google!
 function combine2Words(word1, word2) {
   return word1.concat(word2);
+
 }
 
+//The CONCAT function combines the text from multiple ranges and/or strings.
+
+
 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 + " " + secondWord + " " + thirdWord;
 }
 
 /* 
diff --git a/mandatory/4-tax.js b/mandatory/4-tax.js
index ba77c7ae2..81cf0507f 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(number) {
+  let price = number;
+  return price * 1.2;
+}
 
 /*
   CURRENCY FORMATTING
@@ -17,7 +20,14 @@ function calculateSalesTax() {}
   Remember that the prices must include the sales tax (hint: you already wrote a function for this!)
 */
 
-function addTaxAndFormatCurrency() {}
+function addTaxAndFormatCurrency(number) {
+  let price = number;
+  let percentage = 0.2;
+  const currency = "£";
+  let taxAmount = price * percentage;
+  let totalPrice = price + taxAmount;
+  return ${ currency }${ totalPrice.toFixed(2) }
+}
 
 /* 
 ===================================================