9. Corresponding angles are equal, so technically you can move that (7x - 20) to be diagonal with the (4x + 16). Along with the corresponding angle, diagonal angles are equal to each other. Therefore you can set (7x - 20) equal to (4x + 16) to find x.
7x - 20 = 4x + 16
Solve
3x - 20 = 16
3x = 36
x = 12
Therefore x is equal to 12
<u>Check:</u>
4(12) + 16
= 64
7(12) - 20
= 64
10. All angles in a triangle have to add up to 180 degrees. Therefore, you can write your equation like this: