| $x_{i}$ | 2 | 4 | 6 | 8 | 10 | 12 | 14 | 16 |
| $f_{i}$ | 4 | 4 | $\alpha$ | 15 | 8 | $\beta$ | 4 | 5 |
If the mean and variance of the frequency distribution
\begin{center}
\begin{tabular}{ c c c c c c c c l }
$x_{i}$ & 2 & 4 & 6 & 8 & 10 & 12 & 14 & 16 \\
$f_{i}$ & 4 & 4 & $\alpha$ & 15 & 8 & $\beta$ & 4 & 5 \\
\end{tabular}
\end{center}
are 9 and 15.08 respectively, then the value of $\alpha^{2} + \beta^{2} - \alpha\beta$ is $\_\_\_\_$.