Ten years ago, DEWA, an electricity and water authority, issued $20 million worth of municipal bonds that carried a coupon rate of 6% per year, payable semiannually. The bonds had a maturity date of 25 years. Due to a worldwide recession, interest rates dropped significantly enough for the utility to consider paying off the bonds early at a 10% penalty to the face value. DEWA would then reissue the bonds at the same face value (i.e., $20 million) for the remaining 15 years, but at a lower coupon rate of 2% per year, payable semiannually. What would be the semiannual rate of return to DEWA, if it proceeds with this plan?

Hint: 18%<=i*/six months <=20%