A $25-$year maturity, par bond paying coupons semiannually is callable in $7$ years at a price of $$1,200.$ The bond currently sells at a YTM of $8\%$ per year.

a$.$ What is the yield to call?

b$.$ What is the yield to call if the call price is only $$1,250?$

c$.$ What is the yield to call if the call price is $$1,200$ but the bond can be called in $5$ years instead of $7$ years?