Step by step: The equation for finding a slope is y2 -y1 /X2 - X1 and by x and y it means the coordinates so just pick a random two pair of coordinates and use that equation and if u chose (-1,4) and (1,-4) it will be -4-4/1- -1 which is -4. This works for any 2 coordinates. Sorry if that makes no sense lol
