The smaller triangle and the bigger triangle are similar triangles. The corresponding angles in the similar triangle have the same measurement. That means (3x - 10) is equal to (x + 40)
Solve for x
3x - 10 = x + 40
3x - x = 40 + 10
2x = 50
x = 50/2
x = 25
The value of x is 25, first option