When we add the angle that has x° and the angle that has (4x-20)° we need to get 180°.
Mathematically: x° + (4x-20)° = 180°.
We solve for x:
x°+4x°-20°=180°, we put all numbers that we know on the right side and all unknowns on the left side:
5x°=200°, we divide by 5 and get:
x=40°
So the correct answer is D. x=40°.
