(Bond valuation) Three years ago XYZ International issued some 28?-year ?zero-coupon bonds that were priced with a? market's required yield to maturity of 7 percent and a par value of ?$1,000. What did these bonds sell for when they were? issued? Now that 3 years have passed and the? market's required yield to maturity on these bonds has climbed to 9 ?percent, what are they selling? for? If the? market's required yield to maturity had fallen to 5 ?percent, what would they have been selling? for?