Marty goes to a concert with his friends and wants to buy a t-shirt as a souvenir of the event. He pays the vendor with a $50 bill and gets change back. Later his friend Doc wants to buy a hot pretzel but is 50 cents short. Marty gives him 2 quarters. On the way home, Marty stops and puts gas in his car and pays with his Visa. In which of these transactions did Marty actually use money?
