A 31-L electric radiator containing heating oil is placed in a 48-m3 room. The room and the radiator oil are initially at 14 °C. The barometric pressure in the room is initially 745 mm-Hg. The radiator with a rating of 1.9 kW is then turned on. Heat is lost from the room at a rate of 0.26 kJ/s. After some time, the air temperature has climbed to 28 °C and the oil temperature has increased to 63 °C. If the density of the oil is 950 kg/m3 and its specific heat is 2.2 kJ/kg-°C, how long has the heater been on?