The work done to pull the sled up to the hill is given by
where
F is the intensity of the force
d is the distance where the force is applied.
In our problem, the work done is
and the distance through which the force is applied is 
, so we can calculate the average force by re-arranging the previous equation and by using these data:
where
F is the intensity of the force
d is the distance where the force is applied.
In our problem, the work done is