Answer:

Explanation:
Start by drawing out the triangle on the graph:
(See picture)
(By the drawing you can judge me that I am a really bad artist)
Theta and the side lengths are labeled, the hypotenuse has a length of √21 by Pythagora's theorem. Now, time to put everything to the trigonometric functions:

(Suppose that x is theta as I can't type it)
By some basic understanding that's all that I can do.