this is the formula for calculating a slope

here we have random coordinates that I picked out and what you do is you put in the coordinates Y with Y and X with X you could put it as Y1 and Y2 or Y2 and Y1 but the Xs have to correspond with that too. Now that you have your coordinates in place you just continue with the formula giving you -1 over -3 or simply 1 over 3 because a negative division equals to a positive,