Answer:
x = 25
Explanation:
the exterior angle of a triangle is equal to the sum of the 2 opposite interior angles.
3x - 10 is an exterior angle of the triangle , then
3x - 10 = 25 + x + 15
3x - 10 = x + 40 ( subtract x from both sides )
2x - 10 = 40 ( add 10 to both sides )
2x = 50 ( divide both sides by 2 )
x = 25