If you use a horizontal force of 35.0 N to slide a 13.5 kg wooden crate across a floor at a constant velocity, what is the coefficient of kinetic friction between the crate and the floor?

This is an easy, straightforward problem testing your knowledge of basic definitions of dynamics. What in particular is puzzling you here? Start from the very beginning! A. Can you draw all the forces applied to the crate? B. What does the constant speed mean in terms of the net force applied to the crate? (Net force is the *vector* sum of all the applied forces). C. Do you know how to sum vectors?