i need a mathematic way with some formula to solve it.

and also i want to know how can I solve it by the calculator BA2 Plus

4.3.1 A 10% bond with face amount 100 is callable on any coupon date from 15/2 years after issue up to the maturity date which is 20 years from issue. (a) Find the price of the bond to yield a minimum nominal annual rate of (i) 12%, (ii) 10%, and (iii) 8%. (b) Find the minimum annual yield to maturity if the bond is pur- chased for (i) 80, (ii) 100, and (iii) 120