A person pushes a 18.8-kg shopping cart at a constant velocity for a distance of 31.7 m on a flat horizontal surface. She pushes in a direction 32.2 ° below the horizontal. A 44.9-N frictional force opposes the motion of the cart. (a) What is the magnitude of the force that the shopper exerts? Determine the work done by (b) the pushing force, (c) the frictional force, and (d) the gravitational force.