A rectangular tank is 225 m by 162 m at the base. With what speed must water flow into it through an aperture 60 cm by 45 cm so that the level may be raised 20 cm in 5 hours ?

Volume flown in 5 hours :
$$\eqalign{ & = \left( {225 \times 162 \times \frac{{20}}{{100}}} \right){{\text{m}}^3} \cr & = 7290\,{{\text{m}}^3} \cr} $$
Volume flown in 1 hour :
$$\eqalign{ & = \left( {\frac{{7290}}{5}} \right){{\text{m}}^3} \cr & = 1458\,{{\text{m}}^3} \cr} $$
∴ Required speed :
$$\eqalign{ & = \left( {\frac{{1458}}{{0.60 \times 0.45}}} \right){\text{m/hr}} \cr & = 5400\,{\text{m/hr}} \cr} $$