Here are stock market and Treasury bill percentage returns between 2006 and 2010: Year 2006 2007 2008 2009 2010 Stock Market Return 20.07 10.11 -40.83 32.30 21.86 T-Bill Return 8.30 7.86 3.00 1.40 1.52 a. What was the risk premium on common stock in each year? (Negative values should be indicated by a minus sign. Round your answers to 2 decimal places.) Year 2006 2007 2008 2009 2010 Risk Premium % % % % % b. What was the average risk premium? (Do not round intermediate calculations. Round your answer to 2 decimal places.) Average risk % premium c. What was the standard deviation of the risk premium? (Do not round intermediate calculations. Round your answer to 2 decimal places.) Standard deviation of the risk premium %