Answer: interest rate = 4.85 per year

Working notes for the above answer is as under

Annual Payment  $2,500 a year for 10 years

Present value is $20388.73 today

Now we put all this information in to the formula as follow

PVOA = PMT time ( PVOA Factor = For n = 5Year;i=? per year)

20388.73 = 2500 time ( PVOA Factor = For n = 5Year;i=? per year)

20388.73/2500= ( PVOA Factor = For n = 5Year;i=? per year)

8.1554= ( PVOA Factor = For n = 5Year;i=? per year)

8.155 = PVOA Factor = For n = 5Year;i=4.85 per year