Sketch a Free-Body Diagram. I have a +x direction down the plain and a +y direction upward and perpendicular to the plain. There is a weight, w, on the skier directed straight down, there is a normal force, N, on the skier directed in the +y direction, there is a friction force, f, acting in the -x direction. The inclination of the plain from the horizontal is .

According to Sir Newton:

Since the skier doesn't accelerate in the y direction, :

where m is the mass of the skier.

And

We know that from the y equation, so

where is the coefficient of kinetic friction.

We can divide through by the common m:

As far as the velocity at t = 8.0 s, the acceleration is constant and you know the skier started from rest, so simply apply .

-Dan