Hi Cupcake,
How about I tell you HOW to do it
1) Draw a right angled triangle.
2) Put theta in one of the acute angles.
3) mark the three sides as Opp, adj and hypotenuse. Do you know how to do that?
4) You know that \(sin \theta = \frac{15}{17}\) and that \(sin\theta = \frac{opp}{hyp}\)
so
opp =15 and hyp = 17
put those numbers on your triangle.
5) Use the pythagorean theorum to find the 3rd side.
6) Now look at each of those ratios in turn and see which ones is correct.
Do it a quickly as you can and I will stay around for a little while so you can ask question if you get stuck.