Answer parts b and c and show all your steps please.

6. Risk Premiums. Here are rates of return on a broad stock market index and on Treasury bills between 2011 and 2015: (LO]]-1) Year Stock Market Return (%) T-Bill Return (%) 2011 0.98 0.03 2012 16.06 0.05 2013 33.06 0.07 2014 12.71 0.05 2015 0.67 0.21 a. What was the risk premium on common stock in each year? b. What was the average risk premium? c. What was the standard deviation of the risk premium