We are given two machines in series. The first machine receives an input of 6. We are asked to determine the order of the machines to get a final output of 5. Now, we have to illustrate the problem and arrange the machines in series, input 6 going into the second machine and indicate an output of 5. So we do a balance on machine 2:
In = Out
Input value is 6 and output is 5 plus (the remaining value) x
6 = 5 + x
We need to determine x:
6 = 5 + x
1 = x
So there should be another output, it could be a waste stream of 1 from machine 2 to balance the system.