Explanation:
x°+y°=90°
mSquare =360°
z°= 360°-(90°+90°+51°)
z°=360°-231°
z°=129°
mTriangle=180°
angle in base of triangle is equal
because this is isosceles triangle
so 2y°+z°=180°
2y°+129=180°
2y°=180°-129°
2y°=51°
y°=51°/2
y°=25.5°
x°+y°=90°
so x°=90°-y°
x°=90°-25.5°
x°=64.5°
final
x=64.5°,y=25.5°,z=129°