A liquid of density $750 \mathrm{kgm}^{-3}$ flows smoothly through a horizontal pipe that tapers in cross-sectional area from $A_1=1.2 \times 10^{-2} \mathrm{~m}^2$ to $A_2=\frac{A_1}{2}$. The pressure difference between the wide and narrow sections of the pipe is 4500 Pa . The rate of flow of liquid is $\_\_\_\_$ $\times 10^{-3} \mathrm{~m}^3 \mathrm{~s}^{-1}$.