81. Suppose your car averages 32 miles per gallon on the highway if your average speed is 60 miles per hour, and it averages 25 miles per gallon on the highway if your average speed is 75 miles per hour. a. What is the driving time for a 1500-mile trip if you drive at an average speed of 60 miles per hour? What is the driving time at 75 miles per hour? b. Assume a gasoline price of $2.55 per gallon. What is the cost of gasoline for a 1500-mile trip if you drive at an average speed of 60 miles per hour? What is the cost of gasoline at 75 miles per hour?