A pipe of $0.7$ m diameter has a length of $6$ km and connects two reservoirs A and B. The water level in reservoir A is at an elevation $30$ m above the water level in reservoir B. Halfway along the pipe line, there is a branch through which water can be supplied to a third reservoir C. The friction factor of the pipe is $0.024$. The quantity of water discharged into reservoir C is $0.15 \: m^3/s$. Considering the acceleration due to gravity as $9.81 \: m/s^2$ and neglecting minor losses, the discharge (in $m^3/s$) into the reservoir B is _______.