In a u-tube as shown in a figure, water and oil are in the left...

According to Pascal's law "Pressure applied to an enclosed fluid is transmitted undiminished to every point of the fluid and the walls of the containing vessel." In the given situation as shown in the figure below Pressure due to water column of height $15 \mathrm{ cm}=$ Pressure due to oil column of height $20 \mathrm{ cm}$$\begin{aligned} \Rightarrow \quad \mathrm{h}_{\mathrm{w}} \rho_{\mathrm{w}} \mathrm{g} & =\mathrm{h}_0 \rho_0 \mathrm{ g} \\ 15 \rho_w & =20 \rho_0 \Rightarrow \rho_0=\frac{15}{20} \rho_\omega \\ \rho_0 & =\frac{15}{20} \times 1000\left(\because \text{ given, } \rho_w=1000 \mathrm{ kg} \mathrm{ m}^{-3}\right) \\ & =750 \mathrm{kgm}^{-3} \end{aligned}$