| $x$ | $c$ | $2c$ | $3c$ | $4c$ | $5c$ | $6c$ |
| $f$ | 2 | 1 | 1 | 1 | 1 | 1 |
If the variance of the frequency distribution
\begin{center}
\begin{tabular}{ | c | c | c | c | c | c | c | }
\hline
$x$ & $c$ & $2c$ & $3c$ & $4c$ & $5c$ & $6c$ \\
\hline
$f$ & 2 & 1 & 1 & 1 & 1 & 1 \\
\hline
\end{tabular}
\end{center}
is 160, then the value of $c \in N$ is\\
(1) 7\\
(2) 8\\
(3) 5\\
(4) 6