An estate provides a perpetuity with payments of X at the end of each year. Seth, Susan, and Lori share the perpetuity such that Seth receives the payments of X for the first n years and Susan receives the payments of X for the next m years, after which Lori receives all the remaining payments of X. Which of the following represents the difference between the present value of Seth's and Susan's payments using a constant rate of interest?


a. X[an-vnam]
b. X[¨an-vn¨am]
c. X[an-vn+1am]
d. X[an-vn-1am]
e. X[van-vn+1am]