Answer
$a_{21}=184$
Work Step by Step
Recall:
The $n^{\text{th}}$ term of an arithmetic sequence is given by the formula
$$a_n=a_1+(n-1)d$$
where
$a_1$ = first term
$d$ - common difference
The given arithmetic sequence has:
$a_1=4$
$d=9$
$a_n=184$
To find the value of $n$, substitute the given values into the formula above to obtain:
\begin{align*}
a_n&=a_1+(n-1)d\\
184&=4+(n-1)9\\
184-4&=9(n)-9(1)\\
180&=9n-9\\
180+9&=9n\\
189&=9n
\end{align*}
Divide $9$ to both sides to obtain:
$$21=n$$
Thus, $184$ is the $21^{\text{st}}$ term of the sequence.