Someone help me on Geometric problem. Equations practice.

Answer:
AOB = 36°
Step-by-step explanation:
Because we know that OA is perpendicular with OC so AOC would = 90°
So AOB + BOC = AOC
(6x - 12) + (3x + 30) = 90
6x - 12 + 3x + 30 = 90
6x + 3x + 30 - 12 = 90
9x + 18 = 90
9x = 90-18
9x = 72
x = 8
So to find AOB, we would apply it to the equation:
AOB = 6x - 12
= 48 - 12
= 36°
Hope this helped :3