diff --git a/extra/1-currency-conversion.js b/extra/1-currency-conversion.js
index 75b3c6aab..3e4f3988a 100644
--- a/extra/1-currency-conversion.js
+++ b/extra/1-currency-conversion.js
@@ -5,7 +5,9 @@
   Write a function that converts a price to USD (exchange rate is 1.4 $ to £)
 */
 
-function convertToUSD() {}
+function convertToUSD(price) {
+return price * 1.4;
+}
 
 /*
   CURRENCY CONVERSION
@@ -15,7 +17,9 @@ function convertToUSD() {}
   They have also decided that they should add a 1% fee to all foreign transactions, which means you only convert 99% of the £ to BRL.
 */
 
-function convertToBRL() {}
+function convertToBRL(price) {
+  return price * 0.99 *5.7;
+}
 
 /* ======= TESTS - DO NOT MODIFY ===== 
 There are some Tests in this file that will help you work out if your code is working.
diff --git a/extra/2-piping.js b/extra/2-piping.js
index b4f8c4c1b..7ed5bebe4 100644
--- a/extra/2-piping.js
+++ b/extra/2-piping.js
@@ -16,26 +16,27 @@
   the final result to the variable goodCode
 */
 
-function add() {
-
+function add(a,b) {
+return a + b;
 }
 
-function multiply() {
-
+function multiply(a,b) {
+return a * b;
 }
 
-function format() {
-
+function format(price) {
+return `£` + price ;
 }
 
 const startingValue = 2;
 
 // Why can this code be seen as bad practice? Comment your answer.
-let badCode =
+let badCode = format(multiply(add(startingValue,10),2));
 
 /* BETTER PRACTICE */
-
-let goodCode =
+let addPrice = add(startingValue, 10);
+let multiplyPrice = multiply(addPrice, 2);
+let goodCode = format(multiplyPrice);
 
 /* ======= TESTS - DO NOT MODIFY ===== 
 There are some Tests in this file that will help you work out if your code is working.
diff --git a/mandatory/1-syntax-errors.js b/mandatory/1-syntax-errors.js
index d9e004465..d25d33e08 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;
+  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 9eb8c8cd7..fe5f20cf3 100644
--- a/mandatory/2-logic-error.js
+++ b/mandatory/2-logic-error.js
@@ -1,16 +1,16 @@
 // 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;
+  let total= a * b * c;
+  return total;
 }
 
 /* 
diff --git a/mandatory/3-function-output.js b/mandatory/3-function-output.js
index 5a953ba60..44684c597 100644
--- a/mandatory/3-function-output.js
+++ b/mandatory/3-function-output.js
@@ -2,15 +2,18 @@
 function getRandomNumber() {
   return Math.random() * 10;
 }
+//it gives a random number which is greater than or equal to 0 and less than 10.
 
 // Add comments to explain what this function does. You're meant to use Google!
 function combine2Words(word1, word2) {
   return word1.concat(word2);
 }
+//this function will combine word1 and word2 together.
 
 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..56ecfd59a 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 = 1.2;
+  return price*tax;
+}
 
 /*
   CURRENCY FORMATTING
@@ -17,7 +20,10 @@ function calculateSalesTax() {}
   Remember that the prices must include the sales tax (hint: you already wrote a function for this!)
 */
 
-function addTaxAndFormatCurrency() {}
+function addTaxAndFormatCurrency(price) {
+let product = calculateSalesTax(price);
+return '£' + product.toFixed(2);
+}
 
 /* 
 ===================================================