The center of mass of the refrigerator is located at a height h from the floor in the middle between the supports, the distance between which is equal to l. The rear supports are wheels with negligible friction in the axles, the front supports are fixed projections, the coefficient of friction of which on the floor is equal to µ. If a horizontal force F is applied to the refrigerator at the level of its center of mass, the refrigerator begins to move back towards the wheels. What horizontal force should be applied at the same level in the opposite direction to move the refrigerator forward?