The product would expand to

This is a trinomial, and the only way to make it a binomial is to cancel out a coefficient using our variable
.
So, we can cancel either the linear term or the constant term.
In the first case, we require

In the second case, we require

But
must be a non-zero rational number, so this solution is not feasible.
If you add up all of the money he made and divide it by the amount he made via tips, you will see that the percent tip he received was 16%