| $x_i$ | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| Frequency $f_i$ | 3 | 6 | 16 | $\alpha$ | 9 | 5 | 6 |
If the variance of the frequency distribution
\begin{center}
\begin{tabular}{l l l c l l l l}
$x_i$ & 2 & 3 & 4 & 5 & 6 & 7 & 8 \\
Frequency $f_i$ & 3 & 6 & 16 & $\alpha$ & 9 & 5 & 6 \\
\end{tabular}
\end{center}
is 3, then $\alpha$ is equal to $\underline{\hspace{1cm}}$.