There are three different liquids, with densities ${\rho }_1,{\rho }_2$ and ${\rho }_3$ in a U-shaped container as shown in the picture. The lengths shown are $H_1=15 \mathrm{cm}$ and $H_2=10 \mathrm{cm}$. Which of the following equations gives the correct relation between the densities of the fluids in the container?

An object of weight $W$ has a uniform rectangular cross-section of $a\times 2a$ and density of $0.25 \mathrm{g} {\mathrm{cm}}^{-3}$. Part of it is immersed in water and the rectangle is tilted by $45°$, while one of its corners is just at the water surface. Find the torque of the buoyancy force to the center of mass of the object.