Answer:
a = 53
Explanation:
Start with d
The ends of d + 53 are diameter ends. That means that d + 53 is a right angle
d + 53 = 90
d = 90 - 53
d = 37
Next, find b. The end points of b are the same end points as for 53 degrees. B is the central angle of 53 which means b = 2 * 53
b = 106
c is the supplement of b
c + b = 180
b = 106
c + 106 = 180
c = 180 - 106
c = 74
The triangle containing a and c is isosceles because 2 of the 3 angles are opposite radii. The lowest angle is also a because it is opposite one of the radii.
a + a + 74 = 180
2a = 180 - 74
2a = 106
a = 106/2
a = 53
Hard to believe, but there it is.