A retired person wants to invest an amount of Rs 50000. His broker recommends investing in two types of bonds A and B yeilding 10% and 9% return respectively on the invested amount. He decides to invest at least Rs 20000 in bond A and at least Rs 10000 in bond B. He also wants to invest at least as much in bond A as in bond B. Slove this linear programming problem graphically to maximize his returns.