From the figure, we have three angles on the straight line.
x , x , and 90
Sum of angles on a straight line = 180
x + x + 90 = 180
2x + 9 = 180
2x = 180 - 90
2x = 90
x = 90/2
x = 45
The measure of the angle at which the ray hit the water = 45
The measure of the angle at which the ray reflected from the water = 45