A single-plate clutch has a friction disc with inner and outer radii of $20$ mm and $40$ mm, respectively. The friction lining in the disc is made in such a way that the coefficient of friction $\mu$ varies radially as $\mu=0.01r$, where $r$ is in mm. The clutch needs to transmit a friction torque of $18.85$ kN.mm. As per uniform pressure theory, the pressure (in MPa) on the disc is ________.
