Eduardo has an annuity paying $500.00 at the end of each month for 18 years. The interest rate is r⁽⁴⁾ = 9.125%. After 6 years the interest rate changes to 8.125% (same compounding).

a) What is the effective interest rate per payment period before the rate change?

b) What is the effective interest rate per payment period after the rate change?

c) What is the future value of his annuity? (Be sure to show all the steps and all your formulas.)