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!