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)/(c c)`. Its viscosity is nearly `(n)/(2)` poise. Then find the value of n. Assume `g=980(cm)/(sec^(2))` and neglect the density of air.