Figure 2 . 1 8 shows a network of water pipes with flows measured in liters per minute.
(a) Set up and solve a system of linear equations to find the possible flows.
(b) If the flow through AB is restricted to 5 L/min, what will the flows through the other two branches be?
(c) What are the minimum and maximum possible flows through each branch?
(d) We have been assuming that flow is always positive. What would negative flow mean, assuming we allowed it? Give an illustration for this example.

20. A fi 30 , 10 3 Figure 2.18