For spring break, Melanie will either stay home or go to Daytona Beach. At home, Melanie pays $10 per day for food and earns $90 a day at her job. At Daytona Beach, Melanie will stay with friends and so has no lodging cost. She will pay $20 per day for food. In terms of dollars, Melanie's opportunity cost per day of going to Daytona Beach is how much