I cannot figure out the solution to this homework problem. I tried using excel to build out the formulas but it is still wrong. Help!

ect Question 8 0 / 10 pts Following are three economic states, their likelihoods, and the potential returns: Economic state Probability Return 0.22 15% Fast growth Slow growth 0.55 7% Recession 0.23 -26% Determine the standard deviation of the expected return. (Note: by convention, the standard deviation is shown in percentage. Do not round intermediate calculations and round your answer to 2 decimal places and do not include a % symbol.) 15.29