In order to find slope, you put have four points (x1, y1), (x2, y2). Your formula will be m = (y2-y1) / (x2-x1). Your (y2, y1) will be on top while (x2, x1) will be on the bottom. I hope that is the right formula you need. I always use it and it works for me. Have a great day!! :)