Answer:
AOB = 36
Explanation:
OA is perpendicular to OC
AOB + BOC = 90 ------------equation
where:
AOB = 6x - 12
BOC = 3x + 30
plugin values into the eq.
6x - 12 + 3x + 30 = 90
6x + 3x + 30 - 12 = 90
9x + 18 = 90
9x = 90 - 18
9x = 72
x = 72/9
x = 8
plugin values to AOB = 6x - 12
AOB = 6x - 12
AOB = 6(8) - 12
AOB = 36