A father pushes horizontally on his daughters sled to move it up a snowy incline, as illustrated

Question:

A father pushes horizontally on his daughter€™s sled to move it up a snowy incline, as illustrated in Fig. 5.27b. If the sled moves up the hill with a constant velocity, how much work is done by the father in moving it from the bottom to the top of the hill? (Some necessary data are given in Exercise 6.)