To solve this problem, we need to determine the value of x, which represents the number that Pete added after doubling his original number.
Let's break down the information given:
Pete's original number: 10
Pete doubles his original number: 10 * 2 = 20
Pete adds x to the doubled number: 20 + x
Pete multiplies the sum by 4: 4 * (20 + x) = 120
We can set up the equation as follows:
4 * (20 + x) = 120
Let's simplify and solve for x:
80 + 4x = 120
To isolate x, we subtract 80 from both sides of the equation:
80 + 4x - 80 = 120 - 80
4x = 40
To solve for x, we divide both sides of the equation by 4:
x = 40 / 4
x = 10
The value of x is 10.
The answer is: 10
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
Pete thinks of a number. He doubles it, adds X, multiplies by 4, and ends up with 120. His original number was 10. What is the value of unknown variable X?

### Answer:
