Answer:
A. 53.1
Step-by-step explanation:
I incorporated a drawing of the exercise. In any right triangle we can use three trigonometric functions in order to find the angles that are different to 90 degrees.
This trigonometric functions are :
Sine (sin)
Cosine (cos)
Tangent (tan)
The hint to solve this exercise is to use the inverse tangent. The tangent is define as

In the drawing the opposite side length is 4 and the adjacent side length is 3
⇒
⇒
