carla purchased a 10-year bond with a coupon rate of 7.5% paid semiannually. the bond has a par value of $1,000 and may be called in 7 years for $1,050. the current market price of the bond is $1,015. calculate the bond's yield to call. a) 7.77% b) 7.50% c) 6.75% d) 8.05%