The stated yield to maturity and realized compound yield to maturity of a default free zero-coupon bond are always equal. Why?

Consider a bond with a 10% coupon and yield to maturity = 8%. If the bonds yield to maturity remains constant, then in one year will the bond price be higher, lower or unchanged? Why?

A 20-year maturity, 8% coupon bond paying coupons semiannually is callable in five years at a call price of $1,100. The bond currently sells at a yield to maturity of 7% (3.5% per half-year).

a. What is the yield to call?