A 64.4-kg skier coasts up a snow-covered hill that makes an angle of 21.7 with the horizontal. The initial speed of the skier is 8.43 m/s. After coasting a distance of 1.40 m up the slope, the speed of the skier is 4.07 m/s. (a) Find the work done by the kinetic frictional force that acts on the skis. (b) What is the magnitude of the kinetic frictional force?