A 56.0 kg mass is sliding down a frictionless plane at a speed of 4.20 m/s. A force of 55.0N parallel to the plane acts on the mass to pull it up the plane. When the force has acted over a distance of 6.80 m, the mass has a speed of 5.40 m/s. What change in gravitational potential energy occurred while the force acted on the mass?