An air bubble of diameter 6 mm rises steadily through a solution of density $1750 \mathrm{~kg} / \mathrm{m}^3$ at the rate of $0.35 \mathrm{~cm} / \mathrm{s}$. The co-efficient of viscosity of the solution (neglect density of air) is $\_\_\_\_$ Pas (given, $\mathrm{g}=10 \mathrm{ms}^{-2}$ )
