Two identical parallel discs have a common axis and are located at a distance h from each

Question:

Two identical parallel discs have a common axis and are located at a distance h from each other. The radius of each disc is equal to a, with a >> h. One disc is rotated with a low angular velocity co relative to the other, stationary, disc. Find the moment of friction forces acting on the stationary disc if the viscosity coefficient of the gas between the discs is equal to