An air bubble of radius 1 mm is allowed to rise through a long cylindrical column of a viscous liquid of radius 5 cm and travels at a steady rate of 2.1 cm per sec. If the density of the liquid is 1.47 g/cc. Its viscosity is nearly 2n poise. Then find the value of n. Assume g=980 cm/sec2 and neglect the density of air.