You push on a cart (18.0kg) at a 30 degree below horizontal angle. The coefficient of kinetic friction between the chair and the floor is 0.625. What is the value of the angled force that will keep the chair moving at a constant velocity?

Find the force of friction parallel to the plane using the perpendicular normal force and the coefficient of friction. A force that will keep the chair moving at a constant velocity will create a net zero for all vectors horizontal to the inclined plane.