A counter flow heat exchanger is to het air entering t 4000C with a flow rate of 6 kg/s by the exhaust gas entering at 8000C with a flow rate of 4 kg/s. the overall heat transfer coefficient is 100 W/(m2K) and the outlet temperature of the air is 551.50C. Specific heat at constant pressure for both air and the exhaust gas can be taken as 1100 J/(kgK). Calculate the heat transfer area needed and the number of transfer units.