3. This problem asks you to calculate the actual (as opposed to the expected) real after-tax interest rate using annual data from 1961 to the present. The formula for the actual real after-tax interest rate is

(1 - t)i - p, where i is the nominal interest rate, t is the tax rate, and p is the inflation rate.

Use the data for the United Kingdom. For the nominal interest rate I, take the average for each year of the three-month Treasury securities and measure annual inflation by the CPI inflation rate from December to December of each year. In what periods was the real after-tax interest rate positive? In what periods was it negative?