diff --git a/README.md b/README.md
index 6611d00c3..7743addab 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,6 @@ If you think you need to do more practice with the basics, then you can find som
 
 ## Setting up your code editor
 
-
 There are some tools that will help you to write code. One of these, [Prettier](https://prettier.io/), formats your code, making it easier for you and others to read.
 
 ### 1. Install prettier
@@ -25,10 +24,9 @@ There are some tools that will help you to write code. One of these, [Prettier](
 - Search for `editor format`
 - Set `editor.formatOnSave` and `editor.formatOnPaste` to true
 
-
 ## Running the code/tests
 
-The files for the mandatory/extra exercises are intended to be run as jest tests. 
+The files for the mandatory/extra exercises are intended to be run as jest tests.
 
 - Once you have cloned the repository, run `npm install` once in the terminal to install jest (and any necessary dependencies).
 - To run the tests for all mandatory/extra exercises, run `npm test`
diff --git a/mandatory/1-syntax-errors.js b/mandatory/1-syntax-errors.js
index d9e004465..91b584b6b 100644
--- a/mandatory/1-syntax-errors.js
+++ b/mandatory/1-syntax-errors.js
@@ -1,16 +1,18 @@
 // 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}`;
 }
 
 /* 
@@ -24,7 +26,6 @@ To run the tests for just this one file, type `npm test -- --testPathPattern 1-s
 
 ===================================================
 */
-
 test("addNumbers adds numbers correctly", () => {
   expect(addNumbers(3, 4, 6)).toEqual(13);
 });
diff --git a/mandatory/2-logic-error.js b/mandatory/2-logic-error.js
index 9eb8c8cd7..ff5b064e1 100644
--- a/mandatory/2-logic-error.js
+++ b/mandatory/2-logic-error.js
@@ -1,16 +1,15 @@
 // 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..3f02163a4 100644
--- a/mandatory/3-function-output.js
+++ b/mandatory/3-function-output.js
@@ -2,15 +2,17 @@
 function getRandomNumber() {
   return Math.random() * 10;
 }
+//It gives random number between 0 to 10.
 
 // Add comments to explain what this function does. You're meant to use Google!
 function combine2Words(word1, word2) {
   return word1.concat(word2);
 }
-
-function concatenate(firstWord, secondWord, thirdWord) {
+// It combines 2 words.
+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}`;
 }
 
 /* 
@@ -23,7 +25,6 @@ To run the tests for just this one file, type `npm test -- --testPathPattern 3-f
 (Reminder: You must have run `npm install` one time before this will work!)
 ==================================
 */
-
 test("concatenate example #1", () => {
   expect(concatenate("code", "your", "future")).toEqual("code your future");
 });
diff --git a/mandatory/4-tax.js b/mandatory/4-tax.js
index ba77c7ae2..d915fb92e 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(sales) {
+  const tax = 0.2 * sales;
+  return tax + sales;
+}
 
 /*
   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(sales) {
+  return "£" + calculateSalesTax(sales).toFixed(2);
+}
 
 /* 
 ===================================================