Your moving company runs out of rope and hand trucks, so you are forced to push two crates along the floor as shown in the figure below.

Your moving company runs out of rope and hand trucks, so you are forced to push two crates along the floor as shown in the figure below. The crates are moving at constant velocity, their masses are m1 = 40 kg and m2 = 21 kg, and the coefficients of kinetic friction between both crates and the floor are 0.30. Find the normal force between the two crates.