(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 $36,179.88 that will pay them $4,000 per year for 15 years. They don't have the slightest idea what return they would be making on their investment of $36.179.88. What rate of return would they be earning? %. (Round to two decimal The annual rate of return your folks would be earning on their investment is places.)