Assuming that the 75 feet measurement is the distance from where Justin is at the ground level to the fish (and not the diagonal distance from his location to the fish), the angle is given by arctan(28/75) = 28.472 degrees. This is probably the right answer.
If the 75 feet measurement is the diagonal distance, the angle is arcsin(28/75) = 21.921 degrees.
We know this from a relation of right triangle trigonometry. Tell me if you need more clarification.