PLEASE HELP ME!! I REALLY NEED TO GET THIS DONE :(

Andy and Nick went to the amusement park. They each bought a sandwich, and Nick got a small drink. Andy had a $10 gift certificate to put toward the cost, and Nick paid the rest, which came to $44.50. A ticket costs $20.00, and a sandwich costs $6.50. How much does a drink cost at the amusement park?