x = 28
Explanation:
The angles COE, EOF, and FOB combine to form angle COB
angle COB = (angleCOE)+(angleEOF)+(angleFOB)
angle COB = (3x)+(x)+(x+12)
angle COB = 5x+12
Angles AOD and COB are vertical angles, so they are congruent
angle COB = angle AOD
5x+12 = 152
5x = 152-12
5x = 140
x = 140/5
x = 28