A pension fund has an average duration of its liabilities equal to 15 years. The fund is looking at 5-year maturity zero-coupon bonds and 4% yield perpetuities to immunize its interest rate risk. How much of its portfolio should it allocate to the zero-coupon bonds to immunize if there are no other assets funding the plan?
a) 52
b) 48
c) 33
d) 25