How hard is it to expand a set-covering model to accommodate new cities? Answer this by modifying the model in Figure 6.25. (See the file Locating Hubs with Distances.xlsx.) Add several cities that must be served: Memphis, Dallas, Tucson, Philadelphia, Cleveland, and Buffalo. You can look up the distances from these cities to each other and to the other cities in a reference book (or on the Web), or you can make up approximate distances.

a. Modify the model appropriately, assuming that these new cities must be covered and are candidates for hub locations.

b. Modify the model appropriately, assuming that these new cities must be covered but are not candidates
for hub locations.

Figure 6.25

G H K M N 3 Mile limit (cell $B$4) values along side, output cell(s) along top 5. 800 1 900 7 1000 1 1100 1 1200 1 ol 1 OTTTCsed_as_hub_1 Used_as_hub_2 1. Used_as_hub_3 000oUsed_as_hub_4 Used_as_hub_5 Used_as_hub_6 oUsed_as_hub_7 o Used_as_hub_8 Used as_hub_9 -Used_as_hub_10 Used_as_hub_11 Used_as_hub_12 Total_hubs 3.