1.) Draw a picture (aka- free body diagram) to help visualize the problem.
2.) Break up the forces into necessary components (in green). Note: I have chosen the coordinate system, as indicated in the picture, to simplify the problem.
3.) Newton's Second Law (for x):
4.) Newton's Second Law (for y):
5. Substitute back into the equation derived for :
6. Solve for :
Hopefully that will clear things up! Good luck!