The maximum efficiency of two continuous processes

[Peter Jones]

Homework Statement:

A combination of steam mercury turbines, includes two stages. The first stage runs on saturated mercury vapour at 876°F and emits heat to heat a boiler at 460°F. The vapour in this boiler is used to run a second stage of the turbine, and emits heat to a steam condenser chamber which is at 100°F. Find the maximum efficiency of this combination

Relevant Equations:

Carnot efficiency H=1-T2/T1

I think it reaches its maximum efficiency when it is two continuous Carnot process. Its efficiency then will be H= 1-(W1+W2)/(Q1+Q2), with W1/Q1>=T2/T1 and W2/Q2>=T3/T2 therefore
H<= 1- (Q1.T2/T1+Q2.T3/T2)/(Q1+Q2), that is as far as i can go, have not got a result yet

 

[Chestermiller]

Let Q1 be the heat received by the mercury at 876 F. In terms of Q1, what is the heat Q2 emitted by the mercury to the steam boiler at 460 F? In terms of Q2, what is the heat Q3 condensed in the condenser at 100 F? In terms of Q1, what is the heat Q3 condensed in the condenser at 100 F?