Toyota Corp's stock is $32 per share. Its expected return is 25% and variance is 15%. Honda Corp's stock is $20 per share. Its expected return is 20% and variance is 7%. Benz Corp's stock is $42 per share. Its expected return is 11% and variance 7%. The covariance between Toyota and Honda is 0.03. What would be the standard deviation of a portfolio consisting of 50% Toyota and 50% Honda?

Answer is 0.15, Please explain how to get this and show all steps!