fluid mechanics Questions

In a U-tube, as shown in the figure, the water and oil are in the left side and right side of the tube respectively. The height of the water and oil columns are $15\text{cm}$ and $20\text{cm}$ respectively. The density of the oil is (${\rho }_{water}=1000{\text{kg/m}}^3$):

Two small spherical metal balls, having equal masses, are made from materials of densities ${\rho }_1$ and ${\rho }_2$ such that ${\rho }_1=8{\rho }_2$ and having radii of $r_1$ and $r_2$, respectively. They are made to fall vertically (from rest) in a viscous medium whose coefficient of viscosity equals $\eta$ and whose density is $0.1{\rho }_2$. The ratio of their terminal velocities would be: