Learning this as well.
All triangle's angles equate to 180 degrees.
Also keep in mind that a flat line is 180 degrees as well
The two slashes through the hypotenuse show that both triangles' hypotenuses are equal
(Triangle ADC:
So. 180 - 46 = 134, we know the bottom angle is 90, 134-90= z, z=y
Edit: Also, since the angles line up with each other, you know that the angle on the exact opposite side of the 47 given is also 47, 47+47= 94, 180-94= 86 (total top angle) divide that by two for y.
Y= 42
X= 90