Your classmates from the university of chicago are planning to go to miami for spring break, and you are undecided about whether you should go with them. the round-trip airfare is $600, but you have a frequent-flyer coupon worth $500 that you could use to pay part of the airfare. all other costs for the vacation are exactly $900. the most you would be willing to pay for the trip is $1,400. your only alternative use for your frequent-flyer coupon is for your trip to atlanta two weeks after the break to attend your sister's graduation, which your parents are forcing you to attend. the chicago-atlanta round-trip airfare is $450. what is the opportunity cost of using the coupon for the miami trip?