Question

Two birds sit at the top of two different trees 17.8 feet away from one another. The distance between the first bird and a bird watcher on the ground is 37.4 feet.

What is the angle measure, or angle of depression, between this bird and the bird watcher?

Answer 1

cosx=17.8/37.4
x=61.6

Answer 2

since you have the values of the adjacent and the hypotenuse sides.
use cosine.

cosx=17.8/37.4

I notice your asking many questions about trigonometry.
Try solving it yourself. It would be probably much easier when you learn it than asking it one by one here.

No offense. Just suggesting.