Edit in JSFiddle

/*  
	Formula for volume is LxWxH. Multiply the input by itself three times!
	Or use the Math.pow method(). 
*/

//Lets grab the span ids and store them into variables for later use
var length = document.getElementById("length");
var answer = document.getElementById("answer");

//Ask the user for an input and store into a variable
var side = prompt("Enter the length/height/width of your cube", 2);

//calculate the volume - Method 1
//var volume = side * side * side;
//console.log("side: " + side + " volume: " + volume);

length.innerText = side;

//calculate the volume - Method 2
var volume = Math.pow(side,3);

answer.innerText = volume;
<!-- Easy JavaScript #9 - Calculate Volume of a Cube -->
<p>
How do you get the volume of a Cube? You multiply the length, width, and height. 
</p>
<p>
Since it's a cube, you will only need to get one number. 
</p>
<p>
One side of your cube has a measurement of <span id="length">___</span> units.
</p>
<p>
Your cube has a volume of <span id="answer">___</span> units cubed.
</p>
<p>
Visit <a href="http://www.easyprogramming.net">EasyProgramming.net</a> for more tutorials!
</p>
#length , #answer{
  color: blue;
  text-decoration: underline;
  font-weight: bold;
}