Find the value of x
(6x + 7)°
(8x - 17)°

Explanation:

The two angles shown are vertical angles. This occurs whenever you have an X shape like this, and whenever the angles are opposite one another. Vertical angles are always congruent.

6x+7 = 8x-17

6x-8x = -17-7

-2x = -24

x = -24/(-2)

x = 12

8(-10x+3.5y-7)

8×-10x + 8×3.5y + 8×-7

-80x + 28y - 56

therefore

-80x+28y-56 is the correct answer