“Rate of change” means the same as “slope.”
In algebra, we use the word "slope" to describe how steep a line
is and slope can be found using the ratio rise/run between
any two points that are on that line.
Starting from the point that has the coordinate (-1, -1),
we rise go 1 unit down so our rise is -1 and run 3 units.
So our slope or rise/run is -1/3.