What are the steps on solving this?

17.2 The figure shows a block of mass m=15kg which rests on a surface with coefficient of static friction us A force pulls on the block at an angle 0 - 20% above the horizontal. If the minimum magnitude of the force for which the block will begin to slide is given by F=42N, what is the value of us? (A) 0.3 (B) 0.4 (C) 0.7 X (D) 0.6 (E) 0.5