A. 63.1°
Explanation:
Whatever it may be reflection, rotation or translation, the angle or size of the triangle will not change.
As we know that the sum of angles in a triangle is 180°.
In ΔX'Y'Z', ∠X' + ∠Y' + ∠Z' = 180°
53.8° + 63.1° + ∠Z' = 180°
116.9° + ∠Z' = 180°
∠Z'= 180° - 116.9°
= 63.1°