9. The table below contains the average annual interest rate on three-month Treasury bills (T- bills) and the percentage change in the consumer price index (CPI-U) for 1981, 1984, and 1985 (years of relatively high nominal interest rates) and 2014, 2015 and 2016 (years of relatively low nominal interest rates). 1981 1984 1985 2014 2015 2016 Interest rate on three-month T- 14.03 9.52 7.48 0.03 0.05 0.32 bills Percentage change in the CPI-U 10.38 4.37 3.53 1.61 0.12 1.28 Source: https://fred.stlouisfed.org/ a. What was the real interest rate in the years 1981, 1984, 1985, 2014, 2015, and 2016? b. In which of these years was the real interest highest? In which years was the real interest rate negative