Torque and viscosity relations, fluid mechanics

[abs123456]

A uniform film of oil 0.13 mm thick separates two circular discs, each 150 mm diameter and
mounted coaxially. Find the torque required to rotate one disc relative to the other at a steady speed
of 400 rev/min if the oil has a viscosity of 0.14 Pa.s. (Ignore edge effects at the rim of the disc).

Answer: 2.24 Nm.

Please could you show me the stages of how to go about getting that answer.
I am getting a bit confused with the variables

 

[Curl]

Use the definition of viscosity then integrate in the radial direction.
The oil is very thin so assume laminar flow; should be straightforward after this