In a stack emission measurement at an industry, the stack cross-sectional area at $30$ m height was divided into four equal sectors. The measured velocities and $\mathrm{SO}_{2}$ concentrations through these sectors at this height are given in the table.
The mean $\mathrm{SO}_{2}$ concentration from the stack is $\_\_\_\_$ $\mathrm{mg} / \mathrm{m}^{3}$ (rounded off to two decimal places).
$$\begin{array}{|c|c|c|}
\hline
\begin{array}{c}
\textbf{Sector} \\
\textbf{Number}
\end{array}
&
\begin{array}{c}
\textbf{Velocity} \\
(\mathrm{m/s})
\end{array}
&
\begin{array}{c}
\mathrm{SO}_{2}\ \textbf{Concentration} \\
(\mathrm{mg}/\mathrm{m}^{3})
\end{array}
\\
\hline
1 & 15 & 1000 \\
\hline
2 & 17 & 1150 \\
\hline
3 & 19 & 1250 \\
\hline
4 & 21 & 1275 \\
\hline
\end{array}$$
