IBM has just issued a callable (at par) 5 year, 9% coupon bond with quarterly coupon payments. The bond can be called at par in two years or anytime thereafter on a coupon payment date. It has a price of $102 per $100 face value, implying a yield to maturity of 8.78%. What is the bond's yield to call?

8.78%

6.86%

8.15%

7.91%