How do I find the standard deviation of expected return for stock A

Stocks A and B have the following probability distributions of expected future returns: B Probability 0.1 (8%) 2 (40%) 0 0.3 0.3 11 19 0.2 19 25 0.1 40 37 a. Calculate the expected rate of return, rb, for Stock B (ra = 10.90%.) Do not round intermediate calculations. Round your answer to two decimal places. 10.4 % b. Calculate the standard deviation of expected returns, OA, for Stock A (OB = 20.54%.) Do not round intermediate calculations. Round your answer to two decimal places. 37.88 X % c. Now calculate the coefficient of variation for Stock B. Round your answer to two decimal places. 1.98