## Discrete Mathematics and Its Applications, Seventh Edition

$243$
We are selecting five elements, each of which can be any of the three elements $a$, $b$, $c$, with repetition allowed. There are $3$ choices for the first element, $3$ choices for the second element, and so on. By the product rule on page 386, the total number of ways to select five elements is $3*3*3*3*3=3^5=243$.