Question

solve for x, not sure how to do this

Answer 1

All the angles in a triangle add up to 180:

31+(x-15)+x=180
2x-15=149
2x=164
x=82 degrees

Answer 2

Answer: 82°

Explanation: 

31 + x + x - 15 = 180      (Sum of angles in a triangle is 180)

16 + 2x = 180

2x = 164

x = 82