Gas mileage actually varies slightly with the driving speed of a car (as well as with highway vs. City driving). Suppose your car averages 29 miles per gallon on the highway if your average speed is 47 miles per hour, and it averages 27 miles per gallon on the highway if your average speed is 71 miles per hour. Answer parts (a) and (b) below. A. What is the driving time for a 2400-mile trip if you drive at an average speed of 47 miles per hour? What is the driving time at 71 miles per hour?