Answer:
A ≈ 41.81°
Explanation:
Because this triangle can be defined as a right triangle due to the right angle.
Use inverse sine to calculate the angle using the ratio of the opposite and hypotenuse side.
A = arcsin(opposite/hypotenuse)°
A = arcsin(4/6)°
A = arcsin(2/3)°
A = 41.810314895778...°
A ≈ 41.81°