Can anyone tell me the equation that I should be using for the problem below...


Financial Planning

A retired couple has $40,000 to invest. As their financial consultant, you recommend they invest some money in Treasury bills that yield 6%, some money in corporate bonds that yield 8%, and some money in junk bonds that yield 10%. Prepare a table showing the
various ways the couple can achieve the following goals:

a. They want 42500 per year in income.
b. They want 43000 per year in income.
c. They want $3500 per year in income.