Fluid Mechanics

The surface of water in a water tank of cross section area $750 \mathrm{~cm}^2$ on the top of a house is ' $h$ ' $m$ above the tap level. The speed of water coming out through the tap of cross section area $500 \mathrm{~mm}^2$ is $30 \mathrm{~cm} / \mathrm{s}$. At that instant $\frac{\mathrm{dh}}{\mathrm{dt}}$ is $x=10^{-3} \mathrm{~m} / \mathrm{s}$. The value of ' $x$ ' will be