The graph presented describes the cost of Jasper's rental truck based on the time he uses it. The flat fee of $25 is the initial amount he pays regardless of the time, and the hourly charge of $15 indicates that the cost increases as the number of hours increases.
In the context of the graph, the rate of change represents how much the total cost increases for each additional hour of rental time. Given that Jasper is charged $15 for each hour, the rate of change is $15.
Therefore, the correct interpretation of the rate of change from the options provided is:
15