To find out the concentration of \(\text{SO}_2\) in the air (in parts per million, i.e., ppm), the data was collected for 30 localities in a certain city and is presented below: \(\begin{array}{|c|c|c|c|c|c|c|}\hline \text{Concentration of SO}_2 \text{ (in ppm)} & 0.00 - 0.04 & 0.04 - 0.08 & 0.08 - 0.12 & 0.12 - 0.16 & 0.16 - 0.20 & 0.20 - 0.24 \\ \hline \text{Frequency} & 4 & 9 & 9 & 2 & 4 & 2 \\ \hline \end{array}\) Find the mean concentration of \(\text{SO}_2\) in the air.