Answer:
17 =x
Step-by-step explanation:
These are alternate interior angles and alternate interior angles are equal when the lines are parallel
9x+7 = 10x-10
Subtract 9x from each side
9x+7-9x = 10x-10-9x
7 = x-10
Add 10 to each side
7+10 =x-10+10
17 =x
