6-9. In intermodal transportation, loaded truck trailers are shipped between railroad terminals on special flatbed carts. Figure 6.38 shows the location of the main railroad terminals in the United States and the existing railroad tracks. The objective is to decide which tracks should be "revitalized" to handle the intermodal traffic. In particular, the Los Angeles (LA) terminal must be linked directly to Chicago (CH) to accommodate expected heavy traffic. Other than that, all the remaining terminals can be linked, directly or indirectly, such that the total length (in miles) of the selected tracks is minimized. Determine the segments of the railroad tracks that must be included in the revitalization program. Figure 6.38 Network for Problem 6-9 SE 2000 1300 1100 800 1000 CH (DE) 200 D 2000 2600 780 900 1400 1300 (DA)