You can put this solution on YOUR website! Going from (4,2) to (5,1), as x increases by 1 (from 4 to 5) y "increases" by -1 (decreases by 1 from 2 to 1).
Since one definition of slope is the increase in y as x increases by 1, that means that the slope of line j is .
Since parallel lines have the same slope (if they have a slope at all), that means that every line parallel to j has a slope of .
Wasn't that easy?
