A wastewater is to be disinfected with $35 \: mg/L$ of chlorine to obtain $99 \%$ kill of micro-organisms. The number of micro-organisms remaining alive $(N_t)$ at time $t$, is modelled by $N_t=N_o e^{-kt}$, where $N_o$ is number of micro-microorganisms at $t=0$, and $k$ is the rate of kill. The wastewater flow rate is $36 \: m^3/h$, and $k=0.23 \: min^{-1}$. If the depth and width of the chlorination tank are $1.5 \: m$ and $1.0 \: m$, respectively, the length of the tank (in $m$, round off to $2$ decimal places) is ________