Question 5: Linear programming (20 marks in total) A retired couple has up to $30,000 to invest in fixed-income securities. Their broker recommends investing in two bonds: one AAA bond yielding 8%; the other a B+ bond paying 12%. After some consideration, the couple decides to invest at most $12000 in the B+ rated bond and at least $6000 in the AAA bond. They also want the amount invested in the AAA bond to exceed or equal the amount invested in the B+ bond. What should the broker recommend if the couple wish to maximize their return on investment?