For the M1 angle, we can conclude the size of angle is 90°. Do the angle equation like this :
15x=90
x = 90/15
x = 6
Do the same thing in M2 :
Subtitute the x value to equation, then evaluate the value by using 90 because it's the same.
x+y=90
6+y=90
y=90-6
y=84
M3 value is same, 90°
9z=90
9z/9 = 90/9
z=10
Hope this helps