Answer
$a_{18}=-46$
Work Step by Step
Using $a_n=a_1+(n-1)d$ or the $n$th term of an arithmetic sequence, then,
\begin{array}{l}
a_{18}=5+(18-1)\left( -3 \right)
\\\\
a_{18}=5-51
\\\\
a_{18}=-46
.\end{array}
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