An airport has two runways. Runway 1R serves only large jets, while runway 1L serves only smaller jets. Large jets wishing to use runway 1R arrive at the average rate of 20 per hour, while the smaller jets using 1L arrive at the average rate of 30 per hour. Each runway can handle an average of 60 jets per hour. Unfortunately, it is rather expensive to keep an aircraft airborne while waiting to land. The large jets incur a cost of $25 per minute, while the small jets cost $10 per minute while circling to land. Calculate the total hourly waiting cost for all jets at the airport.

a) With regard to the question above, because of repair work, assume Runway 1L must be temporarily shut down. During this time, all jets will land on runway 1R. Calculate the total hourly waiting cost for all jets at the airport with only this one runway available.

b) With regard to part a., the repair work is now completed and the airport has decided to change its policy on runway usage. Both runways will now be available to either type of jet for landing. What is now the total hourly waiting cost for all jets under this new policy?