When we have a cyclic quadrilateral, a quadrilateral inscribed in a circle, the opposite angles are supplementary, adding to 180 degrees.
We can ignore that expression for y because we're not asked to solve for y. We're asked angle BAD, which is supplementary to BCD, 85, so must be 180-85=95 degrees.
a. 95 degrees
For b and c we have
12 x - 20 + 4x/3 = 180
36 x - 60 + 4x = 540
40 x = 600
x = 15
ABC = 12 x - 20 = 12(15) - 20 = 160 degrees
b. 160 degrees
ADC is supplementary to that, 20 degrees
c. 20 degrees
