If the angle of depression from the pier to the beach is 12 degrees, then the angle of elevation from the beach to the pier is also 12 degrees.
The height of the pier, distance along the beach and distance from the beach to the top of the pier form a right triangle, so we will be able to use trigonometric functions of a right triangle to solve this problem.
The side opposite the angle of elevation is the height of the pier 5 yds. The adjacent side to the angle of elevation is the distance down the beach from the pier we are trying to find.
Tangent (12) = opposite/adjacent = 5/adjacent
so adjacent = 5/tangent(12) = 23.5 yards, which is how far Lauren's sister is diown the beach.