Here are stock market and Treasury bill percentage returns between 2006 and 2010: Stock Market Return Year T-Bill Return 2006 2007 2008 2009 2010 19.67 9.81 -40.63 32.00 21.36 790 7.56 2.80 1.20 1.32 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