Need help finding the standard deviation please!

Assume these are the stock market and Treasury bill returns for a 5-year period: 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? (lgnore that the estimation is from a sample of data.) Answer is complete but not entirely correct. Complete this question by entering your answers in the tabs below. What was the risk premium on common stock in each year? Note: Do not round intermediate calculations. Enter your answers as a percent rounded to 2 decimal places. Negative values should be entered with a negative sign. What was the risk premium on common stock in ezch year? Note: Do not round intermediate calculations. Enter your answers as a percent rounded to 2 decimal places. Negative values should be entered with a negative sign. (x) Answer is complete but not entirely correct. Complete this question by entering your answers in the tabs below. What was the average risk premium? Note: Do not round intermediate calculations. Enter your answer as a percent rounded to 2 decimal places. ( Answer is complete but not entirely correct. Complete this question by entering your answers in the tabs below. What was the standard deviation of the risk premium? (Ignore that the estimation is from a sample of data.) Note: Do not round intermediate calculations. Enter your answer as a percent rounded to 2 decimal places