A 20-year maturity, 7.0% coupon bond paying coupons semiannually is callable in seven years at a call price of $1,200. the bond currently sells at a yield to maturity of 6.0% (3.00% per half-year).

required:
a. what is the yield to call?
b. what is the yield to call if the call price is only $1,150?
c. what is the yield to call if the call price is $1,200 but the bond can be called in four years instead of seven years?