1. Chad had $80 before, since 28.80/36% is 80.
2. Chad has $28.97 left, because what he had left before the dinner was $51.02, $80-28.80=51.02 then, you take the 16.50 with the 16% which in total is 22.05. But once you have that all solved, subtract 51.02 from the dinner bill that is 22.05, and your answer is $28.97.