Triangle XYZ is an isosceles triangle, then ∠Z and ∠X (also called u) measure the same.
The addition of the internal angles of a triangle is equal to 180°:
∠X + ∠Y + ∠Z = 180°
Replacing with ∠X = ∠Z = u, and ∠Y = 112°:
u + 112° + u = 180°
2u + 112° = 180°
2u = 180° - 112°
2u = 68°
u = 68°/2
u = 34°