Problem 3 (25 points) An investement firm is considering four possible investments. Investment 1 will yield a net present value (NPV) of 16000 SGD ; investment 2, an NPV of 22000 SGD; investment 3, an NPV of 12000 SGD; and investment 4, an NPV of 8000 SGD. Each investment requires a certain cash outflow at the present time: investment 1, 5000; investment 2, 7000; investment 3, 4000; and investment 4, 3000. Currently, 14000 SGD are available for investing. (1) (5 points) Formulate an integer linear program that will enable the investment firm to decide which investments to choose so that the NPV of the investment portfolio is maxi- mized.