Answer: angleAOB = 40°
Step-by-step explanation: Drawing these angles, we see that angle AOC is the sum of angle AOB and angle BOC, so:
angleAOC = angleAOB + angleBOC
108 = 3x + 4 + 8x - 28
108 + 24 = 11x
11x = 132
x = 12
Knowing x, to find angleAOB, just substitute and calculate:
angleAOB = 3x+4
angleAOB = 3.12 + 4
angleAOB = 40°
The angle AOB is 40°.