Arithmetic progression: ACT Math Practice Question

Try this ACT math practice question on how to find the terms of an arithmetic progression.

In an arithmetic progression the difference between consecutive terms is a constant. For example, the sequence $3, 7, 11, 15, \ldots$ is an arithmetic progression where the consecutive terms are $4$ apart. If the first term of an arithmetic progression is $4$ and the last term is $54$, and the sum is $609$, then what is the third term?

1. $\quad 8$
2. $\quad 8.5$
3. $\quad 9$
4. $\quad 9.5$
5. $\quad 10$

Choice C