Annual investments are being made so that $20,000 will be accumulated at the end of 10 years. the interest rate on these investments is initially expected to be 4 percent compounded annually. After 4 years, the rate of the interest is unexpectedly increased to 5 percent, so that payments for the remaining 6 years can be reduced. What amounts should be invested annually for the first 4 years and what sums for the last 6?