Practical steam engines utilize 450°C steam, which is later exhausted at 270°C.

(a) What is the maximum efficiency that such a heat engine can have? 

(b) Since 270°C steam is still quite hot, a second steam engine is sometimes operated using the exhaust of the first. What is the maximum efficiency of the second engine if its exhaust has a temperature of 150°C? 

(c) What is the overall efficiency of the two engines? 

(d) Show that this is the same efficiency as a single Carnot engine operating between 450°C and 150°C. Explicitly show how you follow the steps in the Problem- Solving Strategies for Thermodynamics.