List the costs that would likely be included in each of the following marginal-cost calculations.
1. The marginal cost of one additional passenger on an American Airlines flight.
2. The marginal cost of serving one additional customer in a Pizza Hut.
3. The marginal cost of united Airlines adding a flight from Honolulu to Seattle.
4. The marginal cost of keeping a Wachovia branch bank open one additional hour on Saturdays.
5. The marginal cost of manufacturing one additional pair of Nordic skis.