Air at T1=1300 0R, P1=16 lbf/in2 enters a counterflow heat exchanger operating at steady state and exits at P2=14.7 lbf/in2. A separate stream of air enters at T3=850 0R, P3=60 lbf/in2 and exits at T4=1000 0R, P4=50 lbf/in2. The mass flow rates of the streams are equal. Stray heat transfer and the effects of motion and gravity can be ignored. Assuming ideal gas model with Cp=0.24 Btu/lb. 0R, determine (a) T2 in 0R, and (b) the rate of exergy destruction within the heat exchanger, in Btu per lb of air flowing. Let T0=520 0R and P0=1 atm.