A man is pulling two boxes, one on top of the other, up the ramp shown by pulling on a rope parallel to the surface of the ramp. The coefficient of kinetic friction between the ramp and the lower box is 0.444, and the coefficient of static friction between the two boxes is 0.800. With what force does the man have to pull in order to move the boxes up the ramp at a constant speed of 15.0 cm/s?