The mass of a hot-air balloon and its occupants is 260 kg (excluding the hot air inside the balloon). The air outside the balloon has a pressure of 1.01 105 Pa and a density of 1.29 kg/m3. To lift off, the air inside the balloon is heated. The volume of the heated balloon is 600 m3. The pressure of the heated air remains the same as the pressure of the outside air. To what temperature (in Kelvins) must the air be heated so that the balloon just lifts off?