Annuity interest rate)Your folks just called and would like some advice from you. An insurance agent just called them and offered them the opportunity to purchase an annuity for $15, 980.78 that will pay them $2,500 per year for 10 years. They don't have the slightest idea what return they would be making on their investment of $15 comma 980.78. What rate of return would they be earning? The annual rate of return your folks would be earning on their investment is nothing%. (Round to two decimal places.)