Everybody is making something tough out of something easy.
Everybody knows the formula [ Force = (mass) x (acceleration) ]. Right ?
We're supposed to find the force on the skier when the skier is accelerating,
and it gives us the skier's mass. So there you are !
Net force on the skier = (64 kg) x (the skier's acceleration).
It depends on the skier's acceleration, which we're not told.
More acceleration = the result of more net force.
More net force = the cause of more acceleration.
And that is absolutely everything that you can do with the information
that's given in this question.