The envelope and basket of a hot-air balloon have a combined weight of 2.45kN, and the envelope has a capacity (volume) of 2.18 x 103 m3. When it is fully inflated, what should be the temperature of the enclosed air to give the balloon a lifting capacity (force) of 2.67kN (in addition to the balloon's weight)? Assume that the surrounding air, at 20.0oC, has a weight per unit volume of 11.9 N/m3 and a molecular mass of 0.028 kg/mol, and is at a pressure of 1.0 atm.