Answer: a. 
![X[a_(n) -v^(n) a_(m) ]](https://img.qammunity.org/2021/formulas/business/college/23hy7e29fxnlfrk3p4h8r3xhwrzaxqf99j.png)
Step-by-step explanation:
The Present Value of the perpetuity for Seth is denoted by;
= 
 because Seth receives it for n years.
The Present Value of the perpetuity for Susan is denoted by;
= 
 because it is the value after n periods multiplied by the payments received for m periods. 
The result is;
= 
 - 
 
= 
![X[a_(n) -v^(n) a_(m) ]](https://img.qammunity.org/2021/formulas/business/college/23hy7e29fxnlfrk3p4h8r3xhwrzaxqf99j.png)