Thermodynamics Part 5

A Carnot engine (E) is working between two temperatures 473 K and 273 K . In a new system two engines - engine E1 works between 473 K to 373 K and engine E2 works between 373 K to 273 K. If η12,η1 and η2 are the efficiencies of the engines E,E1 and E2 respectively, then