Telephone calls for the YakLine, a discount long distance carrier, are routed through a variety of switching devices that interconnect various network hubs in different cities. The maximum number of calls that can be handled by each segment of their network is shown in the following table:

Network Segments Calls (in 1,000s)

Washington, DC to Chicago ..........800

Washington, DC to Kansas City ........650

Washington, DC to Dallas ...........700

Chicago to Dallas .............725

Chicago to Denver .............700

Kansas City to Denver ...........750

Kansas City to Dallas ............625

Denver to San Francisco ..........900

Dallas to San Francisco ............725

YakLine wants to determine the maximum number of calls that can go from their east coast operations hub in Washington, DC to their west coast operations hub in San Francisco.

a. Draw a network flow model for this problem.

b. Create a spreadsheet model for this problem and solve it.

c. What is the optimal solution?