First one.
Since the two angles are congruent through vertical angles theorem,
5x = 6x - 8
5x - 6x = -8
-x = -8
x = 8
Second one.
Use the 180° rule.
(8x - 2) + (2x + 2) = 180
8x - 2 + 2x + 2 = 180
8x + 2x + 2 - 2 = 180
10x = 180
x = 180 / 10
x = 18
Third one.
Vertical angle theorem.
7x = 5x + 40
7x - 5x = 40
2x = 40
x = 40 / 2
x = 20
