how did you get 10.88%

Expected returns and Standard Deviations: Use the following information on states of the economy and stock returns to calculate the expected return for Dingaling Telephone: State of Economy Probability of State of Economy Security Return if State Occurs Recession Normal Boom 0.25 0.30 0.45 1.00 -5% 10% 22% b) Using the information in the previous question, calculate the standard deviation of return