The Organ Procurement and Transplantation Network (OPTN) is under contract with the U.S. Department of Health and Human Services to coordinate organ donation, procurement, and transplantation services throughout the U.S. As part of this process, it is interested in identifying an optimal number of designated liver transplant centers among a subset of 21 cities. The data file (see Data \#3 tab) includes information on the linear distances (in miles) between the 21 cities. How many centers are needed, and in which cities should they be located, so that residents of all 21 cities served by OPTN are within 800 miles of at least one transplant center (assume a linear model)