Please help me on how to get the standard deviation, I already got all the answers. Please explain how you get the standard deviation answer and the equation you used. Thank you!

Assume these are the stock market and Treasury bill returns for a 5-year period: Stock Market T-Bill Return Return (%) (%) Year 2013 34.30 0.15 2014 14.00 0.15 2015 -3.90 0.15 2016 15.10 0.10 2017 24.50 0.12 Required: 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? (Ignore that the estimation is from a sample of data.) Complete this question by entering your answers in the tabs below. Required A Required B Required C What was the risk premium on common stock in each year? (Do not round intermediate calculations. Enter your answers percent rounded to 2 decimal places.) Year Risk Premium 2013 2014 2015 2016 2017 34.15 % 13.85 % (4.05) % 14.95 % 24.35 %