Doris has $20,000 to invest. Her financial planner recommends that she diversify into three investments:
Treasury bills that yield 5% simple interest,
Treasury bonds that yield 7% simple interest, and corporate bonds that yield 10% simple interest.
Doris also wishes to earn $1,390 per year in income.
Also, Doris wants her investment in Treasury bills to be $3,000 more than her investment in corporate bonds.
How much money should Doris place in each investment?