Answer:
A) x = 20
Explanation:
The horizontal line is a straight angle, so it is 180°, and the angles on the left is right, so it is 90°.
180 - 90 = 90, which means the two smaller angles total up to 90°.
So, 90 = 4x - 10 + x
Simplify: 90 = 5x - 10
Add: 100 = 5x
Divide: x = 20