\textbf{64.} In the circuit shown below, the ideal voltmeter reads $8.4$ V. What is the ratio of the output power of battery (2) to the input power of battery (1)?
\textit{[Figure: Circuit with two batteries: $\varepsilon_1$, $r_1 = 2\,\Omega$ and $\varepsilon_2 = 12\,\text{V}$, $r_2 = 1\,\Omega$, connected with a $2\,\Omega$ resistor and a voltmeter V between them]}
\begin{itemize}
\item[(1)] $1$
\item[(2)] $2$
\item[(3)] $\dfrac{6}{5}$
\item[(4)] $\dfrac{9}{7}$
\end{itemize}