Hi, Im redoing a bathroom and replacing the tub surround. The wall behind only has greenboard about 3 ft up from the tub and some of the paper came off when I took the old surround out. Do I need to cut out the dry wall and greenboard out where I put in the new surrond? Thanks

If your putting a new fiberglass surround in its place, then no. If your going to tile the tub area then you should replace the drywall w/ cement board.