A power of \(60 \mathrm{~kW}\) is transmitted by a multi-plate clutch at \(1500 \mathrm{rpm}\). The axial intensity of pressure is not to exceed \(15 \mathrm{MPa}\). The coefficient of friction for the friction surfaces is 0.15 . The external radius of friction surface is \(120 \mathrm{~mm}\) and internal radius is \(100 \mathrm{~mm}\). Find the number of plates required to transmit the power of \(60 \mathrm{~kW}\).