take any two points, subtract the y values and divide it by the difference in the respective x values
(y1 - y2)/(x1 - x2)
let's say I use points (0,-11) and (2,17)
I would just plug in the values
(-11 - 17) / (0 - 2)
simplify, and you get 14 (-28/-2 = 14)
note that you could interchange the two points, just make sure that the x and y values are respective of each other
(y1 -y2 )/(x1-x2) = (y2 - y1)/(x2 - x1) will solve the question similarly
but
(y1 - y2) / (x2 -x1) will not get you the right answer