required for each project (in millions of dollars) are as follows. There are conditions that limit the investment alternatives: - At least two of projects 1,3,5, and 6 must be undertaken. - If either project 3 or 5 is undertaken, they must both be undertaken. - Project 4 cannot be undertaken unless both projects 1 and 3 also are undertaken. The budget for this investment period is $220 million. Max s.t. constraint on projects 1,3,5, and 6 constraint on projects 3 and 5 constraint on projects 1 and 4 constraint on projects 3 and 4 budget constraint (b) Solve the model formulated in part (a). What is the optimal net present value (in millions of dollars)? $ million Which projects will be undertaken? (Enter your answer as a comma separated list of numbers. Use 1 for project 1,2 for project 2,3 for project 3,4 for project 4,5 for project 5 , and 6 for project 6.) How much of the budget is unused (in millions of dollars)? $ million