Find angle a2 which is 40 degrees because it is parallel to angle c.
Find the total of d1 and d2.
total of d1 and d2: 180 - 40 - 40 = 100 degrees
Find d1 and d2 separately.
100 divided by 2 = 50 degrees
Use d1 to find b1 to find total of a1 and a2.
b1 is parallel to d1 so b1 = 50 degrees
a1 and a2 = 180 - 50 - 50 = 80 degrees
a1 = 80 divided by 2 = 40
Since a1 and c1 are parallel due to alternate angles, c1 is 40 degrees
Find b2 now which requires you to do total - minus all angles in the triangle with angle b2.
180 - 40 - 50 - 40 = 50 degrees (angle b2)
AOB has b1 and a1.
40 + 50 = 90 degrees (a1 + b1 = AOB)
The answer is 90 degrees
