a $20-$year, $10\%$ semi$-$annual coupon bond is callable in five years at a call price of $1,200.$ The bond currently sells at a YTM of $6\%.$

a$.)$ what is the yield$-$to$-$call $($YTC$)?$

b$.)$ what is the YTC if the price is only $1,100?$

c$.)$ what is the YTC if the call price is $1,100$ but the bond can be called immediately instead of five years?