\textbf{187.} At an altitude of about 3000 meters above sea level, the air pressure is $68\,\text{kPa}$. This pressure is how many centimeters of mercury?
$$\left(\text{density of mercury} = 13.6\,\frac{\text{g}}{\text{cm}^3},\quad g = 10\,\frac{\text{N}}{\text{kg}}\right)$$
\begin{itemize}
\item[(1)] $60$
\item[(2)] $55$
\item[(3)] $50$
\item[(4)] $45$
\end{itemize}