The diameter of an air bubble which was initially $2 \mathrm{~mm}$, rises steadily through a solution of density $1750 \mathrm{~kg} \mathrm{~m}^{-3}$ at the rate of $0.35 \,\mathrm{cms}^{-1}$. The coefficient of viscosity of the solution is _________ poise (in nearest integer). (the density of air is negligible).