Explanation:
Intersecting secant angles theorem: The angle between two secants is half the difference of the intersected arcs.
52 = ½ (x − 38)
x = 142
Arc angles add up to 360.
360 = 80 + 38 + z + x
z = 100
Tangent-chord theorem: The angle between a tangent and a chord is half the intercepted arc angle.
y = x/2
y = 71