notice the table of values
when x = 2, y = -5
then "x" goes 2 units over to 4, and "y" moves over to 5, now from -5 to 5 is 10 units, so when "x" moved just 2 units, "y" went 10.
then "x" goes further down to 7, moving 3 units over,
and "y" goes further from 5 to 20? what the? it went 15 units.
so.... hmmm notice, is we do some quick splitting and instead check how much "y" is moving for every unit on "x".
notice, on 2 units of "x", "y" moved 10 units
and on 3 units of "x", "y" moved 15 units, like from 5 to 20.
so, "y" is really moving 5 units on every unit moved by "x", so the "rate of change" or slope is indeed constant, is 3 to 1 all the way.