A reversible heat engine $$(E)$$ operating in a cycle interacts with three reservoirs $$1,$$ $$2$$ and $$3$$ maintained at temperature $${T_1} = 500K,$$ $${T_2} = 400K,$$ and $${T_3} = 300K,$$ respectively. The engine receives $$10$$ $$kJ$$ of heat from reservoir $$1$$ and rejects $$3$$ $$kJ$$ to reservoir $$3.$$ The net work output, $${W_{net}}$$ (in $$kJ$$) from the engine is