A $1000 par value 6% bond with semiannual coupons is callable at par five years after issue. It is sold to yield 7% semi-annual under the assumption that the bond will be called. The bond is not called and it matures at the end of 10 years. The bond issuer redeems the bond for 1000 + X without altering the buyers yield rate of 7% convertible semiannually. Find X.

the answer is 58.65 

Please explain the answer