Verified answer

The formula for work is:

W=Fd (where F is the force parallel to the displacement d)

Since there is no friction and since the speed is constant, we only apply force to compensate for gravity. Only the force parallel to the slope will contribute to work done on the skier.

The total gravitational force on the skier is:

F=ma=mg=78*9.8 N

The part of this force (P) which acts in the direction of the slope is:

P=F*tan(30°) (sketch the situation to see why)

So the work required is:

W=P*60≈26 kJ

If anything was unclear, draw a figure and place out force vectors.