In the manufacture of nitric acid, ammonia and preheated air are mixed to form a gas containing 10.0 mole% NH3 at 600°C. The ammonia is then catalytically oxidized to form NO2, which is absorbed in water to form HNO3. If ammonia enters the gas blending unit at 25°C at a rate of 520 kg/h and heat is lost from the mixer to its surroundings at a rate of 7.00 kW, determine the temperature to which the air must be preheated.