Both x and y are inscribed angles. The value of an inscribed angle is half the measure of its intercepted arc. This means that x has a value of 33°, and y has a value of 48°. That means that, according to the triangle angle sum theorem, the third angle has to equal 180 - 33 - 48 = 99°.
This angle is vertical with angle z, so angle z also equals 99°
