A friend called wanting help putting together some very old quilt squares that her grandmother had done. She had just found them stuffed in a drawer. Can someone help me figuring how much yardage she will need to make sashing and backing? She has 20 13" squares. I was thinking maybe 2" sashing between the squares, with a 3 or 4" border, plus the backing all in bleached muslin... I need help! I usually just do baby quilts and don't have to worry about not having purchased enough fabric at one time. I want this to turn out special for her, so I'm coming to y'all for help!