An industrial company is seeking your help to improve their distribution system. The distribution network consists of: four manufacturing facilities in U.S., Canada, and Mexico, seven major distribution centers (DCs) in New York, San Francisco, Los Angeles, Atlanta, Chicago, Dallas and Washington D.C., as well as 13 smaller regional DCs in cities such as Salt Lake City, Minneapolis, St. Louis, Houston, etc. Note that each major DC supports the distribution of products in its local area as well as one or more regional DCs (except for Washington, D.C. distribution center which does not support any regional DCs). Thus, the major DCs are referred to as "parents" while the regional DCs are referred to as "children