The mass of hot-air balloon and its occupants is 320 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 650 m3. The pressure of the heated air remains the same as that of the outside air. To what temperature (in K) must the air be heated so that the balloon just lift off? The molecular mass of the air is 29 u.