A $2\mathrm{.}1-$in$.$ diameter shaft is supported by two sleeves, each of length $=3in.$ as shown. The internal diameter of the sleeves is $2\mathrm{.}2$ in $.$ The radial space between the shaft and the sleeves is filled with an oil of viscosity $=810-3lb-\frac{s}{f}t2.$ If the shaft is rotated at a speed of $600$ rpm $,$ the viscous torque $($ft$-$lb$)$ on the shaft is most nearly