part a) please

3. Consider a situation where your model includes binary variables x1,x2,,x9, each representing the potential purchase of a particular investment. Show how to represent each of the following constraints as a single linear constraint: a. You must choose exactly 4 of them. b. If you choose investments 1 and 2 , you must also choose investment 4 . c. You must choose either both investments 5 and 6 , or neither of them