Help with Geometry and Trig ratios

Question

A surveyor wishes to measure the width of a trench. He places a transit telescope in a position on one side of the trench that is 18 feet higher than the second location. The surveyor reads the angle of depression from the transit telescope and finds that it is 31°, as shown in the diagram below.

If the transit telescope is 4.5 feet above the ground at the first location during this reading, how wide is the trench?

Answer 1

The first transit on one side of the trench is 18 ft higher than the other side of the trench. The transit is set at 4.5 above ground, therefore the transit lens is 18' + 4.5' = 22.5' above the location on the other side of the trench. The angle of depression is the angle formed by the horizontal and the line of sight to the other side and it is given as 31°. This forms a right angle triangle with height of 22.5' and an interior angle of 31°, Then

tan( 31°) = Height / base, with the base representing the width of the trench

base = Height / tan(31°) = 22.5' / tan(31°) = 37.45' is the width of the trench