Question:
Texmart is a locally owned big-box retail store chain in Texas with 75 stores, primarily located in the DallasFort Worth area. In order to compete with national big-box store chains, Texmart is planning to undertake several sustainability (i.e., green) projects at its stores. The national chains have been heavily publicizing their sustainability efforts, including the reduction of greenhouse gas (GHG) emissions, which has had a positive effect on their sales. They have also demonstrated that sustainability projects can have a positive impact on cost (especially energy) savings. The projects Texmart is considering include installing solar panels at some or all of its stores; installing small wind turbines; replacing some or all of its 165 trucks with more fuel-efficient hybrid trucks; reducing waste, including recycling; and reducing plastic bags in their stores. The costs for these projects, the resulting reduction in GHG emissions, the energy savings, and the annual costs savings are shown in the following table:
The media public/relations score in this table designates the importance of a particular project relative to the other projects in generating public awareness and publicity. For example, a score of 3 indicates that the solar power project will have the greatest public impact. However, Texmart believes if it undertakes a project, it will require a threshold number of projects to make an impactspecifically, a solar power installation at 1 store or more, wind power projects at least 3 stores, at least 10 new trucks, at least 2 waste/recycling store projects, and at least 6 stores with plastic bag reduction projects. Texmart has budgeted $30 million for sustainable projects, and it wants to achieve GHG emission reductions of at least 250,000 metric tons per year; it wants to achieve annual cost savings of at least $4 million; and, it wants to achieve annual energy savings of at least 5 million kilowatt hours (kWh), while maximizing the public relations impact of its sustainability program. Develop and solve a linear programming model to help Texmart determine how many projects of each type it shouldundertake.
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Sustalnable Projects SolaWind Shipping Waste Plastic Power Power Vehicles Recycling Bags Media/public relations score Cost GHG reductions (metric 2,600,000 950,000 17,500 8,600 38,000 25 365,000 175,000 900 1.700 tons per year) Cost savings (S) Energy savings (kWh) Units 220,000 25,000 26,000 400,000 50,000 34,000 165 75,000 1.200 75 45,000 55,000 75 75 75