ANSWER
a=53°
b=106°
c=74°
d=37°
EXPLANATION
A semicircle creates a right angle on the circumference.
d+53°=90°
d=90°-53°
d=37°
Angle subtended at the center by an arc is twice the angle subtended at the circumference by the same arc.
c=2d
c=2(37)
c=74°
Adjacent angles on a straight line add up to 180°
c+b=180°
b=180°-c
b=180°-74°
b=106°
The sum of interior angles in an isosceles triangle is 180°
a+a+c=180°
2a+74=180
2a=180-74
2a=106
a=53°
