A trust officer at the Blacksburg National Bank needs to determine how to invest $100,000 in the following collection of bonds to maximize the annual return.

Bond A B C D E
Annual Return 9.5% 8.0% 9.0% 9.0% 9.0%
Maturity Long Short Long Long Short
Risk High Low Low High High
Tax-Free Yes Yes No Yes No

The officer wants to invest at least 50% of the money in short-term issues and no more than 50% in high-risk issues. At least 30% of the funds should go in tax-free investments and at least 40% of the total annual return should be tax free.
a. Formulate an LP model for this problem.
b. Create a spreadsheet model for this problem and solve it using Solver.
c. What is the optimal solution?