13-13. Four proposals are under consideration by your company. Proposals A and C are mutually exclusive; proposals B and D are mutually exclusive and cannot be implemented unless proposal A or C has been selected. No more than $140,000 can be spent at time zero. The before-tax MARR is 15% per year. The estimated cash flows are shown in the accompanying table. Form all mutually exclusive combinations in view of the specified contingencies, and formulate this problem as a linear integer programming model. (13.9) End Proposal of year ABCD 0 −$100,000 −$20,000 −$120,000 −$30,000 1 40,000 6,000 25,000 6,000 2 40,000 10,000 50,000 10,000 3 60,000 10,000 85,000 19,000