Ok so this is summer homework...its hard?

so 3 guys walk in to a restaurant. each meal is 10 dollars (there will be no tax), each person orders 1 meal so grand total is $30. the chef says give them 5 dollars back because they were funny (dont ask) so the waiter says how am i gunna give em each 5 dollars. so he takes 2 dollars and gives em each 1 dollar so if you think of it each of them only paid 9 dollars. so 3x9=27... 27 plus the 2 the waiter took equals 29... what happened the $1?