Assume these are the stock market and Treasury bill returns for a 5-year period: Year 2011 2012 2013 2014 2015 Stock Market Return (%) -34.63 31.40 14.86 3.08 19.26 T-Bill Return (%) 3.90 0.30 0.25 0.10 0.12 c. What was the standard deviation of the risk premium? (Do not round intermediate calculations. Enter your answer as a percent rounded to 2 decimal places.) Standard deviation %