equilibrium giving me some trouble

[mikeman19]

I just got done doing about 20 other problems but I can't figure this one out....

A uniform plank, with a length L of 7.63 m and a weight of 420 N, rests on the ground and against a frictionless roller at the top of a wall of height h = 5.21 m. The plank remains in equilibrium for any value of q= 70° or more, but slips if q < 70. Find the coefficient of static friction between the plank and the ground.

Any help would be appreciated

[Doc Al]

Start by identifying all the forces acting on the plank. Draw a diagram.

Then realize that the plank is in equilibrium, so:
∑Fx = 0
∑Fy = 0
∑Torques = 0 (about any point)