Solve this question with using excel (spreadsheets) with detailed explanations and show the excel formulas and solutions steps.

(PS: Table also can be reach in book "Optimization Modeling with Spreadsheets" at page 289-290)

11. Locating Emergency Service Bases The Southeast Emergency Management Agency is planning to establish a number of helicopter bases in a hurricane-prone part of the country. There are 25 sites under consideration, but the agency has funds to install only three bases. Using a specialized map, the agency has identified counties that can be served from each site in less than 15 minutes of response time. (This response time is considered the maximum desired for the purposes of servicing life-and-death emergencies that might follow a hurricane.) The data describing the potential sites consist of a census list and an accessibility matrix. The census list gives the population of each county. The accessibility matrix contains a 1 as its (k,j) th element if county k can be serviced from a base at site j within 15 minutes. At present, the agency has funds to install just three of the bases, and it wishes to maximize the population served by the bases. At which sites should the bases be established and what is the corresponding population served