Basic Physics Problem. Please Help

[pvwill18]

A 71.8-kg skier coasts up a snow-covered hill that makes an angle of 25.1 ° with the horizontal. The initial speed of the skier is 8.84 m/s. After coasting a distance of 2.10 m up the slope, the speed of the skier is 3.41 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?

Part a= -1761 J

I Just cant figure out how to find part b

[physicsnoob93]

What is the definition of work done?

[pvwill18]

Work done is equal to KE+PE so kinetic energy final + mgh- kinetic energy intial+ mgh where kinetic energy is 1/2mvsquared

[physicsnoob93]

There is another definition of work done which says
W=r \cdot F

Try it now.