The rush-hour traffic flow for a network of four one-way streets in a city is shown in Figure 2. The numbers next to each street indicate the number of vehicles per hour that enter and leave the network on that street. The variables x1, x2. 4. and x4 represent the flow of traffic between the four intersections in the network. For a smooth flow of traffic, we assume that the number of vehicles entering each intersection should always equal the number leaving. For example, since 1,500 vehicles enter the intersection of 5th Street and Washington Avenue each hour and x1 + x4 vehicles leave this intersection, we see that x1 + x4 = 1.500.

(A) Find the equations determined by the traffic flow at each of the other three intersections.
(B) Find the solution to the system in part A.
(C) What is the maximum number of vehicles that can travel from Washington Avenue to Lincoln Avenue on 5th Street? What is the minimum number?
(D) If traffic lights are adjusted so that 1,000 vehicles per hour travel from Washington Avenue to Lincoln Avenue on 5th Street, determine the flow around the rest of the network.

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700 800 600 600 Washington Ave. 900 l 400 Sth St. 500 500 Lincoln Ave. 6th St.