The return of stock A over a given period has a mean of 8% and standard deviation of 5%. The return of stock B has a mean of 16% and standard deviation of 20%. The correlation coefficient of the two returns is 0.3. An investor starts with $4000, short sells $2000 worth of stock A and invests $6000 in B. What's the standard deviation of the portfolio rate of return? Report a decimal here and keep 3 digits after the decimal point