Explanation:
the inner top vertex angle seems to be 90°, so x = 90° too. all angles around a single point in one side of a line are in total 180°.
also, remember, all angles inside a triangle always sum up to 180°.
so, the third inner angle of the triangle is
180 - 90 - 40 = 50°.
that makes z = 180 - 50 = 130°
and y = 180 - 40 = 140°.