Question

What is the value of x?

Answer 1

Short Answer x = 40
Argument
x and 4x - 20  are supplementary. (That means they add to 180 degrees) I think that is the simplest way to do it.

Givens
x
4x - 20 
These two angles add to 180 degrees

Equation
x + 4x - 20 = 180          combine like term on the left
5x - 20 = 180                add 20 to both sides.
5x = 180 + 20
5x = 200                       Divide by 5
x = 200/5
x = 40 <<<<<<<<<<<<Answer

Answer 2

X and (4x - 20) are supplementary angles because they add up to 180°. You can tell this because the line which they are formed on is 180°.

Knowing that x + (4x - 20) = 180, you can solve for x:
x + (4x - 20) = 180
(x + 4x) - 20 = 180
5x - 20 = 180
5x = 200
x = 40°

------

Answer: x = 40°