...

Question 3. Shown in the figure is a system of 4 one way streets leading into the center of a city. The numbers in the figure denote the average number of vehicles per hour that travel in the directions shown. A toal of 300 vehicles enter the area and 300 vehicles leave the area every hour.

Signals at intersections A,B,C and D are to be timed in order to avoid congestion, and this timing will determine flow rates x1, x2, x3, and x4

a) If the number of vehicles entering an intersection per hour must equal the number of vehicles leaving the intersection per four, describe the traffic flow rates at each intersection with a system of equations.

b) If the signal at intersection C is timed so that x3 = 100, find x1, x2, and x4

Here is a link to the diagram for this problem...

http://putfile.com/pic.php?pic=5/13300110940.jpg&s=f5
Like I said the final is monday so any help is much appreciated, thanks!