A girl riding a bicycle along a level road at 12 m/s decides to speed up. She does 8 kJ of work while moving 250 m along the road. At that time she is moving at 17 m/s. Specifications are: frame = 70 N, girl = 560 N, each tire = 13 N, the wheel radius is 46 cm and the height of the center of gravity of the girl above the ground is 75 cm. What is the average force of friction on the girl during the motion? Treat the wheels as thin rings.