Answer:
B) 10
Step-by-step explanation:
Exterior angle property: Exterior angle equals the sum of opposite interior angles.
12x + 10 = -10 + 7x + 70 {Subtract 10 from both sides}
12x = -10 + 7x + 70 - 10
12x = -10 + 70 - 10 + 7x {Combine like terms}
12x = 50 + 7x {Subtract 7x from both sides}
12x - 7x = 50
5x = 50 {Divide both sides by 5}
x = 50/5
x = 10
