A survey was conducted by a group of students as a part of their environment awareness programme, in which they collected the following data regarding the number of plants in 20 houses in a locality. Find the mean number of plants per house. \( \begin{array}{|c|c|} \hline \text{Number of plants} & \text{Number of houses} \\ \hline 0 - 2 & 1 \\ \hline 2 - 4 & 2 \\ \hline 4 - 6 & 1 \\ \hline 6 - 8 & 5 \\ \hline 8 - 10 & 6 \\ \hline 10 - 12 & 2 \\ \hline 12 - 14 & 3 \\ \hline \end{array} \)