Steel balls used in ball bearings are quenched by suddenly dropping the hot balls in a cold oil bath. Steel balls of 50kg mass initially at 200oC and with specific heat 0.45 kJ/kg-K are quenched in an oil bath of initial temperature 30oC and specific heat 2.8 kJ/kg-K. During the quenching, a paddle-wheel driven by a 200 W motor is activated to stir the oil. Thermal equilibrium is established after 20 minutes, when the final temperature is 40oC. Determine the mass of the oil and the entropy generated during the process. Consider the tank containing the oil to be well insulated and of negligible mass.