Answer:
65°
Step-by-step explanation:
Exterior angle of a triangle equals the sum of opposite interior (remote) angles.
3x - 10 = x + 15 + 25
3x - 10 = x + 40
Add 10 to both sides,
3x = x + 40 + 10
3x = x +50
Subtract 'x' from both sides,
3x- x = 50
2x = 50
Divide both sides by 2
x = 50÷ 2
x = 25
Exterior angle = 3x -10
= 3*25 - 10
= 75 - 10
= 65°
