The Fellsway Bank is considering placing ATM machines in the town centers of some of the following six communities: Arlington, Belmont, Cambridge, Winchester, Stoneham, and Melrose. The bank would like to purchase the minimum number of ATM machines needed to ensure that at least one ATM location is within a ten-minute drive from the center of each of these six communities. The times required to drive between the communities are shown in the table below. Driving times (in minutes) between the centers of six communities Belmon Cambridg Wincheste Stoneha Melros Town Arlington t e r m e Arlington 0 Belmont 5 50 5 10 15 20 0 8 10 15 Cambridge 10 8 0 15 20 Winchester 15 10 15 0 10 Stoneham 20 15 20 10 0 Melrose 15 12 10 12 12 120220 15 (a) What is the optimal number of ATM locations for the bank to select? (b) Revisit the model and vary the driving time floor from 5 minutes to 20 minutes and construct a chart to display the optimal number of ATMs in each case.