Assume these are the stock market and Treasury bill returns for a 5-year period: T-Bill Return (%) 1.70 0.20 0.13 0.05 0.07 Stock Market Year 2011 2012 2013 2014 2015 Return (%) 37.13 28.40 17.06 1.08 16.16 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.) Answer is complete but not entirely correct. Standard deviation 28.44 %