-2
y2-y1/x2-x1
take the y coordinate of the second pair of coordinates and subtract it by the y coordinate of the first pair, then take the x coordinate from the second pair of coordinates and subtract it from the x coordinate from the first pair. then put your answer from the y coordinate over the answer from the x coordinates. 1 - 13 / 8 - 2, then you get -12/6, which simplifies to 2.
Hope this helps :)
