Serial Bonds and TIC in Excel. The City of Bedford Falls issues a serial bond of $90,000 to be paid over five years, receiving $89,000. The series of annual payments (including both interest and principal repayment at the end of each year) is as follows: $15,600; $15,700; $23,600; $22,900; $28,700.Using the TIC approach, what is the effective interest rate?