A cart is pulled a distance D on a horizontal surface while it is acted on by five forces, as shown in the diagram. Normal forces of magnitudes N1 and N2 are directed upwards at the rear and front wheels, respectively. Rolling frictional forces of magnitudes f1 and f2 are opposite in direction to the displacement and act on the rear and front wheels, respectively. The weight of the cart, with magnitude W, is directed downward. Finally, a pulling force of magnitude P makes and angle of φ with horizontal. The direction of the displacement is to the right in the diagram. Write an expression for the total work done by the forces of rolling friction and the pulling force. Write your answer will be in terms of the symbols introduced in the problem statement.