When I'm asked to find work done by air resistance against a skier on a slope, will I have to do:

Question

Wr = -Fr*d

or is it affected by an angle:

Wr = -Fr*d*cosTHETA

I was thinking that it isn't because air resistance isn't a specific force acting at one spot but everywhere on the slope at the same time, unless it's what's acting on the skier himself, then I would have to add the angle into my calculations