ANSWER:
[tex]\begin{gathered} a_n=18-3(n-1) \\ a_{100}=-279 \end{gathered}[/tex]
STEP-BY-STEP EXPLANATION:
We have the following sequence:
[tex]18,15,12,9\ldots[/tex]
Therefore, the sequence is:
[tex]a_n=18-3(n-1)[/tex]
Now, when n is 100:
[tex]\begin{gathered} a_{100}=18-3(100-1) \\ a_{100}=18-297 \\ a_{100}=-279 \end{gathered}[/tex]
