Assume these are the stock market and Treasury bill returns for a 5-year period: Year Stock Market Return (%) T-Bill Return (%) 2016 31.80 0.03 2017 11.00 0.03 2018 1.70 0.03 2019 13.10 0.21 2020 21.40 0.23 Required: What was the standard deviation of the risk premium? (Ignore that the estimation is from a sample of data.)