Answer: 26.6 °
Step-by-step explanation:
1) You can draw a triangle with the unknown angle, the horizontal distance covered and the vertical diving distance.
2) In that triangle, the vertical distance is opposite to the angle unknown and the horizontal distance is adjacent to the same angle.
3) Then you can use the trigonometric ratio tangent to relate the three variables:
tan (α) = opposite-leg / adjacent-leg = 50m / 100m = 0.5
4) The tangent equal to 0.5 is not a notable value, so you should use the inverse tangent function that is included in every scientific calculator:
=> α = arc tan(0.5) ≈ 26.6 °