To go from point A (1,6) to B (7,-3),
the x-value goes from 1 to 7, so it increases by 6.
the y-value goes from 6 to -3, so it decreases by 9.
However, this is if it goes ALL the way from A to B. If it only goes 2/3 of the way, then
the x-value only increases by 6 * 2/3, or 4.
the y-value only decreases by 9 * 2/3, or 6.
From point A, we can increase the x-value by 4 and decrease the y-value by 6.
(1 + 4, 6 - 6)
(5,0) is the coordinate of the point 2/3 of the way from A to B
