Finding coefficient of static friction...?

The coefficient of friction is the level of friction that different materials exhibit is measured by the formula � = f / N, where � is the coefficient of friction, f is the amount of force that resists motion, and N is the normal force. Normal force is the force at which one surface is being pushed into another. If a rock that weighs 50 newtons is lying on the ground, then the normal force is that 50 newtons of force. The higher � is, the more force resists motion if two objects are sliding past each other.