Answer:
Step-by-step explanation:
In Javascript, you can accept an input value by using the prompt() function and saving the input into a variable. In the following lines of code, I have declared the three variables at the beginning and then prompted the user to enter a value for each and saved the values in the correct variables. In Javascript length is a keyword so I used len instead.
let base, height, len;
base = prompt("Enter Base value: ");
height = prompt("Enter Height value: ");
len = prompt("Enter Length value: ");