Milk flowing through a stainless steel inner tube ($40 \textit{ mm}$ inner diameter) of double tube-type heater is to be heated from $10^\circ C$ to $85^\circ C$ by saturated steam condensing at $120^\circ C$ on the outer surface of the inner tube. Total heat transferred $(Q)$ is $146200 \textit{ kcal h}^{-1}$ and the overall heat transfer coefficient is $750 \: \textit{kcal h}^{-1} m^{-2} $$^\circ C^{-1}$. The total length of the heating tube in $m$ (rounded off to one decimal place) is __________