120. practice: making calculator.

file: exercise3.zip

// Make a Calculator! using prompt(), and variables, make a program that does the following:
// 1. Prompts the user for first number.
// 2. Stores that first number
// 3. Prompts the user for the second number.
// 4. stores that number and responds with the SUM by using an alert.

// BONUS: Make a program that can subtract, multiply, and also divide!