A trauma center keeps ambulances at locations throughout the east side of a city in an attempt to minimize the response time in the event of an emergency. The times, in minutes, from the ambulance locations to the population centers are below:

Ambulance: East, N.East, S. East, Central

Locations

Site 1: 12, 8, 9, 13

Site 2: 10, 9, 11, 10

Site 3: 11, 12, 14, 11

Site 4: 13, 11, 12, 9

Find the optimal assignment of ambulance to population centers that will minimize the total emergency response.