In the Analysis of Traffic Flow, a Certain City Estimates

Multiple Choice

In the analysis of traffic flow, a certain city estimates the following situation for the "square" of its downtown district. In the following figure, the arrows indicate the flow of traffic. If x₁ represents the number of cars traveling between intersections A and B, x₂ represents the number of cars traveling between B and C, x₃ the number between C and D, and x₄ the number between D and A, we can formulate equations based on the principle that the number of vehicles entering an intersection equals the number leaving it. That is, for intersection A we obtain ​ Formulate equations for the traffic at B, C, and D. Solve the system of these four equations.
​ ​

A)
B) ,
C)
D)
E)