Suppose you are the CFO of Southland Hospital, and your organization issues a 25-year bond that has a 3.75 percent coupon paid semiannually and a face value of $55 million. Four years later, the bond is trading for $52 million. The hospital has a call provision that allows you to call the bond 15 years after issuance, at a price of $57.0 million. Investors currently require a 5.5 percent rate of return and expect you to call the bond.

-What is the number of periods (NPER) in your calculation?