Answer with explanation:
We know that the rate of change in a function is given by :-

Let x denotes the Number of hours and y denotes the Cost of parking .
Here , x- independent variable
y- dependent variable
Now, rate of change = 

Here , the rate of change = $ 2 per hour.
Again rate of change = 

Here , the rate of change = $ 1 per hour.
Since both rate of changes are not equal , it means the rate of change is not constant.