A shaft with outside diameter of \(18 \mathrm{~mm}\) turns at 20 revolutions per second inside a stationary journal bearing \(60 \mathrm{~mm}\) long. A thin film of oil \(0.2 \mathrm{~mm}\) thick fills the concentric annulus between the shaft and journal. The torque needed to turn the shaft is \(0.0036 \mathrm{~N} \cdot \mathrm{m}\). Estimate the viscosity of the oil that fills the gap.