Answer:
30
Explanation:
Exterior angle property: Exterior angle equals sum of interior opposite angles.
5x + 30 + 3x + 40 = 7x + 80
5x + 3x + 30 + 40 = 7x + 80
8x + 70 = 7x + 80
Subtract 70 from both sides
8x = 7x + 80 - 70
8x = 7x + 10
Subtract 7x from both sides
8x - 7x = 10
x = 10
7x + 80 = 7*10 + 80 = 70 + 80 = 150
7x +80 +∠ ACB = 180 {linear pair}
150 + ∠ACB = 180
∠ACB = 180 - 150 = 30