The given graph shows the cost for renting a post hole digger from a local hardware store. We have to determine the rate of change or cost per day.
Let us consider any two points.
Let us consider (1,30) and (2,60)
We have to determine the rate of change which is basically termed as "slope".
Rate of change is expressed as a ratio between a change in one variable relative to a corresponding change in another variable.
Therefore, rate of change or cost per day =
Change in y Change in x
=
= 30
Therefore, the rate of change or cost per day is $30 per day.