\textbf{234 –} If in a dry cell, methanol is used as fuel, the sum of the values x, y, and z in the half-reaction:
$$a\,CH_3OH(\text{l}) + b\,H_2O(\text{l}) \to x\,CO_2(\text{g}) + y\,H^+(\text{aq}) + ze^-$$
what is the value from balancing?
\begin{center}
(1) $6$ \qquad (2) $7$ \qquad (3) $12$ \qquad (4) $13$
\end{center}