I am not sure if I am doing these sets of problems totally wrong or not. If you could please check my answers that would be great!

List the costs that would likely be included in each of the following marginal-cost calculations.

1. The marginal cost of adding a flight from Syracuse to Miami.

A: Cost of jet fuel, food on plan, care of airplane

2. The marginal cost of keeping a travel agency open one additional hour on Saturdays

A: Cost of electricty, salaries, air conditioning

3. The marginal cost of manufacturing one additional pair of water skis.

A: Time spent making another product, raw material needed for water skis, more labor

4. The marginal cost of one additional passenger on a jet flight.

A: Cost for extra saftey equipment, food

5. The marginal cost of serving one additional customer in a resturant.

A: Time, cost of food, Salaries