What is the best trading strategyin constructing and managing a portfolio to achieve the specified objectives? And why?

Portfolio Objectives

Ensure long-term income to meet long-term payments

Maximize returns within the scope of objective 1.

Current holdingsFace Value (AUD)

Cash9,000,000

Bank bills

30 days10,000,000

60 days10,000,000

90 days5,000,000

120 days15,000,000

150 days0

180 days0

Bonds

CGS - 5.75% 15.05.20210

CGS - 5.75% 15.07.20220

CGS - 5.50% 21.04.20230

CGS - 4.75% 21.04.20270

CGS - 3.25% 21.04.20290

CGS - 4.50% 21.04.20331,000,000