Find the mode of the following classified data.
\[ \begin{array}{|c|c|c|c|c|} \hline \text{Class interval} & 0\text{-}10 & 10\text{-}20 & 20\text{-}30 & 30\text{-}40 \\ \hline \text{Frequency} & 3 & 4 & 6 & 5 \\ \hline \end{array} \]
| \(\text{Length (in mm)}\) | 70-80 | 80-90 | 90-100 | 100-110 | 110-120 | 120-130 | 130-140 |
|---|---|---|---|---|---|---|---|
| \(\text{Number of leaves}\) | 3 | 5 | 9 | 12 | 5 | 4 | 2 |