(30 points) Consider a supply chain network with three potential sites for warehouses and five retailer regions. The fixed costs of building warehouses at the three sites are: Site 1: $100,000 Site 2: $90,000 Site 3:120,000 The capacity of each warehouse is 3000 , 2800, and 4000 , respectively. The demands of retailers are given in the following table: ] The unit transportation costs are given in the table below: The operation cost for each site is $20 /unit, $15/ unit, and $19/ unit for sites 1,2 , and 3 , respectively. The company plans to select at least two sites for building warehouses. Formulate the problem as a mixed integer programming model. Define the decision variables, list the constraints, and formulate the objective function. (30 points) Consider a supply chain network with three potential sites for warehouses and five retailer regions. The fixed costs of building warehouses at the three sites are: Site 1: $100,000 Site 2: $90,000 Site 3:120,000 The capacity of each warehouse is 3000 , 2800, and 4000 , respectively. The demands of retailers are given in the following table: ] The unit transportation costs are given in the table below: The operation cost for each site is $20 /unit, $15/ unit, and $19/ unit for sites 1,2 , and 3 , respectively. The company plans to select at least two sites for building warehouses. Formulate the problem as a mixed integer programming model. Define the decision variables, list the constraints, and formulate the objective function