an investor is considering three types of investments: a high-risk venture into oil leases with a potential return of 15%, a medium-risk investment in bonds with a 9% return, and a relatively safe stock investment with a 5% return. he has $50, 000 to invest. because of the risk, he will limit his investment in oil leases and bonds to 30% and his investment in oil leases and stock to 50%. how much should he invest in each to maximize his return, assuming investment returns are as expected?