A pension fund has 30 million dollars to invest. The money is to be divided among treasury notes, bonds and stocks. The rules for administration of the fund require that at least 3 million dollars be invested in each type of investment, at least half the money be invested in treasury notes and bonds and the amount invested in bonds not exceed twice the amount invested in treasury notes. The annual yields for the various investments are 7% for the treasury notes and 8% for bonds and 9% for stocks. How the money should be allocated among the various investments to produce the largest returns.