Mr. Jones has $14,000 to invest in three types of stocks, low-risk, medium-risk, and high-risk. He invests according to three principles. The amount invested in low-risk stocks will be at most $2,000 more than the amount invested in medium-risk stocks. At least $6,000 will be invested in low and medium- risk stocks. No more than 11,000 will be invested in medium- and high - risk stocks. The expected yields are 6% for low risk stocks, 7% for medium risk stocks, and 8% for high fish stocks. How much money should mr. Jones invest in each type of stock to maximize his total expected yield?