Answer:
19 tables, f(19) = $280
1 table, f(1) = $33
Explanation:
Let f(x) be the money Serenity makes each day, where x is the number of tables she serves.
Her saily income includes a fixed injcome of $20/day, plus $13/table in tips.
We can write f(x) = $20 + $13x
When x = 19, f(19) = $280
When x = 1, f(1) = $33