Pedro lives in the dorms and works as a barista at Starbucks. He earns $15 an hour and can work as many hours as he wants. He is considering the possibility of selling coffee to this dorm mates. His mother gave him an espresso machine when he left home for college. He can brew 30 cups of coffee an hour. He would buy the coffee grounds from a local retailer. The cost of the grounds for a cup of coffee would average $0.10 per cup. What is the opportunity cost for Pedro to sell a cup of coffee to one of this dorm mates?