Hello, amberkraidich!

Suppose you live about 5.1 miles away from a tower.

From your home, you see a plane directly above the tower.

Your angle of elevation from the plane is 21º.

What is the plane's altitude? If you make a sketch, a trig relation should suggest itself. Code:

P *
| *
| *
a | *
| *
| 21° *
T * - - - - - - - - - - - * H
5.1

Your house is at $\displaystyle H$; the tower is at $\displaystyle T.\quad HT = 5.1\text{ miles}$

The plane is at $\displaystyle P.\quad PT = a\text{ miles}$

Relative to $\displaystyle \angle H = 21^o$, we have: .$\displaystyle opp\:=\:a,\;\;adj \:=\: 5.1$

What trig function is suggested?