An investor will receive an annuity of $4000 a year for 10 years. The first payment is to be received five years from today. At a 9% discount rate, this annuity's worth today is closest to?A. $16684
B. 18186
C. 25671

CFA level 1 note中的一道题。

还想请问，如何准确地确定期数n的值？