slope is the vertical rise over the horizontal rise
if you select two points on the line -- I used (10, 0) and (20, 20) -- and subtract the y-values you will get the vertical rise (20 - 0 = 20); if you now subtract the x-values (20 - 10 = 10) you will get the horizontal rise
so, 20/10 or 10/1
if you go from point (10, 0) to (20, 20) then you go up by 10 and over to the right by 1
