An investor plans to invest 65 percent of her funds in the common stock of Mickey Company and 35 percent in Mini Company. The expected return on Mickey is 16 percent and the expected return on Mini is 12 percent. The standard deviation of returns for Mickey is 20 percent and for Mini is 15 percent. The correlation between the returns for Mickey and Mini is -0.5 (negative 0.5). Determine the standard deviation of returns for this investor's portfolio.
A. 15.63%
B. 11.33%
C. 21.76%
D. 13.93%