05 kg box rests on a plank that is inclined at an angle of 21 above the horizontal.

A 1.05 kg box rests on a plank that is inclined at an angle of 21° above the horizontal. The upper end of the box is attached to a spring with a force constant of 17 N/m, as shown in the figure. If the coefficient of static friction between the box and the plank is 0.79, what is the maximum amount the spring can be compressed and the box remain at rest?

http://general.physics.rutgers.edu/gifs/CJ/10-8.jpg