Objective: How can you save 100 dollars on an Airplane flight?

Which of the following solutions is more sound in terms of naive physics reasoning?

pick from the following. -- Book your vacation during the month of your birthday and you'll get a hundred dollars added to the trip with Delta.. -- Book your vacation during the month of your birthday and you'll get a hundred dollars off the trip with Delta..
Book your vacation during the month of your birthday and you'll get a hundred dollars off the trip with Delta.