From the data {2,5,8,10}, you have found that the mean is 6.25. Computing the variance then involves accumulating and averaging the squared differences of each data value and this mean. Then
\begin{align*}
& \frac{1}{4} \left ( (2-6.25)^2 + (5-6.25)^2 + (8-6.25)^2 + (10-6.25)^2 \right ) \\
& = \frac{18.0625 + 1.5625 + 3.0625 + 14.0625}{4} \\
& = \frac{36.75}{4}\\
& = 9.1875.
\end{align*}