Three boxes are lined up so that they are touching each other on a nearly frictionless plane. Box A has a mass of mA = 21.0 kg, box B has a mass of m; = 27.5 kg, and box C has a mass of mg = 50.5 kg. An external force F pushes on box A toward the right, and the force that box B exerts on box C has a magnitude of 190 N. Ignore friction. What is the magnitude of the acceleration a of the boxes? What is the magnitude F of the external force? \"1'11