Washington County includes six towns that need emergency ambulance service. Because of the proximity of some of the towns, a single station may serve more than one community. The stipulation is that the station must be within 15 minutes of driving time from the towns it serves. The table below gives the driving times in minutes among the six towns.

Formulate an ILP whose solution will produce the smallest number of stations and their locations. Find the optimum solution.

Time in minutes from i to j 18 60 5S 32 20 12 t0 23 24 24 13 19 S5 18 10 19 20 17 12