Answer:
1) in 25 years, the pension fund should equal:
future value = present value x (1 + interest rate)ⁿ
FV = $20,000,000 x (1 + 8.5%)²⁵ = $153,735,247
2) the value in 12 years = $20,000,000 x (1 - 30%) = $14,000,000
future value = present value x (1 + interest rate)ⁿ
$153,735,247 = $14,000,000 x (1 + interest rate)¹³
(1 + interest rate)¹³ = $153,735,247 / $14,000,000 = 10.981
¹³√(1 + interest rate)¹³ = ¹³√10.981
1 + interest rate = 1.2024
interest rate = 1.2024 - 1 = 20.24%
3) if the fund only earns 6%, in 13 years it will be worth:
FV = $14,000,000 (1 + 6%)¹³ = $29,860,996
so you need $153,735,247 - $29,860,996 = $123,874,251 more
we need to use the future value of an annuity formula:
FV of an annuity = annuity payment x annuity factor
annuity payment = $123,874,251 / 18.882 = $6,560,441