Viscosity is the property of

If the terminal speed of a sphere of gold (density=$19.5 {\mathrm{kgm}}^{-3}$) is$0.2 {\mathrm{ms}}^{-1}$ in a viscous liquid (density=$1.5 \mathrm{kg} {\mathrm{m}}^{-3}$), find the terminal speed of a sphere of silver (density=$10.5 \mathrm{kg} {\mathrm{m}}^{-3}$) of the same size in the same liquid.