The viscosity of a fluid is to be measured by a viscometer constructed of two $100-cm-$long concentric cylinders. The outer diameter of the inner cylinder is $15cm,$ and the gap between the two cylinders is $1mm.$ The inner cylinder is rotated at $300rpm,$ and the torque is measured to be $0\mathrm{.}8N.$ Determine the viscosity of the fluid.

The viscosity of the fluid is

$N-\frac{s}{m^2}$