Formulate the above as a mathematical programming problem with the objective of maximizing annual return on investment subject to the constraints cited above. Show step-by-step solution: objective function, decision variables, constraints, formulation of programming model in Excel and solution in solver.

Problem 4. Firm specializes in recommending oil stock portfolios. - At least two Texas oil firms must be in portfolio. - No more than one investment can be made in foreign oil. - Exactly one of two California oil stocks must be purchased. - If British Petroleum stock is included in portfolio, then Texas-Trans Oil stock must also be included in portfolio. - Client has $3 million available for investments and insists on purchasing large blocks of shares of each company for investment. - Objective is to maximize annual return on investment