A corporation issues a 20 year bond with the final redemption value equal to the face value of $1000, and semiannual coupons of 8.5%. However, the bond is callable at the end of 10 years at $1100, and at the end of 15 years at $1040. What is the price of the bond if the investors yield (the yield-to-worst) is 7.5%? (no excel pls)