Two wooden crates rest on top of one another. The smaller top crate has a mass of m1 = 16.0 kg and the larger bottom crate has a mass of m2 = 90.0 kg. There is NO friction between the crate and the floor, but the coefficient of static friction between the two crates is ?s = 0.77 and the coefficient of kinetic friction between the two crates is ?k = 0.6. A massless rope is attached to the lower crate to pull it horizontally to the right (which should be considered the positive direction for this problem).
what is the frictional force the lower crate exerts on the upper crate in (N)?