Suppose that an investor needs $15,000 at the end of seven years from today. However, he can only invest $1000 per year from year 1 to year 4 (the investments will take place at the end of each year). How much the investor needs to invest each year from year 5 to 7 to achieve his objective (investments will take place at the end of each year)? Assume that the interest rate is 10% compounded annually.

Please include calculations and formulas. Thanks