Problem 8-7 Portfolio risk and return Here are returns and standard deviations for four investments. Standard Deviation Return (8) 3.5 11.5 14.5 21.0 Treasury bills Stock P Stock Stock R ces 0 11 24 22 Calculate the standard deviations of the following portfolios. a. 50% in Treasury bills, 50% in stock P. (Enter your answer as a percent rounded to 2 decimal places.) Standard deviation %