an ice cream truck sells ice cream between 2 p. m. and 10 p. m. each night in the summer. at the end of the night, the driver calculates his profits and makes a graph to analyze the data. what is the average rate of change for the data from the 5th hour to the 8th hour? be sure to include the correct units of measurement.

7 hours
−7 dollars per hour per hour
21 dollars
−21 dollars per hour per hour