Stock A has a standard deviation of returns of 21% and Stock B has a standard deviation of returns of 20%. Suppose you decide to invest all of your investment funds in these two stocks, and 39% is invested in Stock A. The correlation coefficient of returns for these two stocks is 0.21. What is the standard deviation of returns for the combined investment in these two stocks? (Answer to the nearest tenth of a percent (i.e., 12.3 but do not use the % sign).