L electrical radiator containing heating oil is placed in a 50-m^3 room. both the room and the oil in the radiator are initially at 10 C. The radiator with a rating of 1.8 kW is now turned on. At the same time, heat is lost from the room at an average rate of 0.35 kJ/s. After some time, the average temperature is measured to be 20 C for the air in the room, and 50 C for the oil in the radiator. Taking the density and the specific heat of the oil to be 950 kg/m^3 and 2.2 kJ/kg*C, respectively, determine how long the heater is kept on. Assume the room is well-sealed so that there are no air leaks.