A commuter regularly drives 70 miles from home to work, and the amount of time required for the trip varies widely as a result of road and traffic conditions. The average speed for such a trip is a function of the time required. For example, if the trip takes 2 hours, then the average speed is
miles per hour.
(a) What is the average speed if the trip takes an hour and a half? (Round your answer to three decimal places.)
(b) Find a formula for the average speed s as a function of the time t required for the trip.