What is the annualized theoretical spot rate for a 1.5-year maturity if the annualized yields on zero-coupon six-month and one-year Treasury securities are 2.85% and 4.61%, the 1.5-year security has an annual coupon rate of 5.5%, pays coupons semiannually, and sells at par? Report your answer to the nearest 0.001%. E.g., if your answer is 5.5875%, record it as 5.588.