please explain

Isabel prefers to purchase bonds that contain a sinking fund provision to protect her from any potential loss of her invested capital. She purchased a 20-year, $20,000 sinking fund bond with a 12% coupon, paid seml-annually, for $18,900. If the company calls the bond after 10 years, and the call penaity requires a payment of $30 per $1,000 of face value, what are the nominal and effective ylelds to call on this bond? a) 12.77% and 13.18%, respectively b) 12.81% and 13.22%, respectively c) 13.01% and 13.43%, respectively d) 13.16% and 13.59%, respectively