The surface of water in a water tank of cross section area 750 cm^2 on the top of a house is h m above the tap level. The speed of water coming out…

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