A lorry of mass 12,000 kg moves up a straight hill of length 500 m, starting at the bottom with a speed of 24 m s^-1 and reaching the top with a speed of 16 m s^-1. The top of the hill is 25 m above the level of the bottom of the hill. The resistance to motion of the lorry is 7500 N. Find the driving force of the lorry.