A skier going down a hill accelerates from 5.15m/s to17.3m/s over a period of 11.7 seconds. For all calculations, you may neglect drag.

If the skier’s total mass is 57.3kg, what is the average force applied by the snow against the skis to bring her to a stop?

would it be:

f=(57.3kg)(17.3-5.15)/11.7

I'm not sure what formula to use