Moira inherited $20,000 and invested part of it in a money market account, part in municipal bonds, and part in a mutual fund. After 1 year, she received a total of $1,220 in simple interest from the three investments. The money market account paid 4% annually, the bonds paid 5% annually, and the mutual fund paid 8% annually. There was $4,000 more invested in the mutual fund than in money market account. Find the amount that Moira invested in mutual fund?