Someone plz look at my code?!

// 1. Attach this file -- math.js -- to the index.html file using a <script> tag

// 2. Add an alert to announce the program with a message like "Let's do some math!"
alert("lets do some math");
// 3. Create a variable and use the prompt() method to collect a number from a visitor
var first_number = prompt("Enter a number");
// 4. Convert that value from a string to a floating point number
    first_number = parseFloat(first_number);
// 5. Repeat steps 3 and 4 to create a second variable and collect a second number
var second_number = prompt("Please enter another number");
    second_number = parseFloat(second_number);
// 6. Create a new variable -- message -- which you'll use to build
//    a complete message to print to the document
//    Start by creating a string that includes <h1> tags as well
//    and the two input numbers. The string should look something like this:
//    "<h1>Math  with the numbers 3 and 4</h1>" where the two numbers are
//    the values input from the user. Use string concatenation to create this
//    and make sure you actually perform the math on the values by 
//    using the + symbol to add their values together
var message = "<h1>Math with the numbers " + first_number + " and " + second_number + "</h1>"; 
// 7. Add another string to the message variable. 
//    The string should look something like this after concatenation:
//    "3 + 4 = 7"
message += num1 + " + " + num2 + " = " + num1 + num2;
// 8. Add a linebreak tag -- <br> -- to the message variable

// 9. Continue to add to the message variable to include strings
//    demonstrating multiplication, division and subtraction
//    For example:
//    "3 * 4 = 12"
//    "3 / 4 = 0.75"
//    "3 - 4 = -1"

// 10. Use the document.write() method to print the message variable 
//     to the web page. Open the finished.png file in this workspace
//     to see what the completed output should look like
document.write(message);