\textbf{184.} In the circuit below, the equivalent resistance between points M and N is $\dfrac{R}{2}$. How many ohms is $R$?
\textit{[Figure: Circuit with an $18\,\Omega$ resistor in the top branch, three resistors $R$ in series in the middle branch between points M and N, and one resistor $R$ in the bottom branch, all connected in parallel between M and N.]}
\begin{itemize}
\item[(1)] $18$
\item[(2)] $12$
\item[(3)] $6$
\item[(4)] $3$
\end{itemize}