14. Payments of X are made at the beginning of each year for 20 years. These payments
earn interest at the end of each year at an annual effective rate of 8%. The interest is
immediately reinvested at an annual effective rate of 6%. At the end of 20 years, the
accumulated value of the 20 payments and the reinvested interest is 5600.
Calculate X.
(A) 121.67
(B) 123.56
(C) 125.72
(D) 127.18
(E) 128.50

给的答案是 20个X和21个interest pmt 为什么interest不是20个呢？
谢谢！