Treasury securities that mature in 6 years currently have an interest rate of 8.5%. Inflastion is expected to be 5% each of the next three years and 6% each year after the third year. The maturity risk premium is estimated to be 0.1% (t-1), where t is equal to the maturity of the bond (i.e. the maturity risk premium of a one year bond is zero). The real risk free rate is assumed to be constant over time. What is the real risk free rate of interest?