Physics help needed: Potential energy and work?

A wooden block placed at the end of a flat wooden board of length L begins to slide down the board when it is tilted at an angle of 37 degrees from the horizontal. The block slides at a constant speed all the way to the other end of the board. (a) What is the change in potential energy of the block when it goes from the high end to the low end? (b) What is the work done against the force of friction? (c) Explain why your answers to (a) and (b) are the same or different. What assumptions are you making in this problem?