Five years ago you created a portfolio. You put 30% of your money in Stock A and 70% of your money in Stock B. The returns for Stock A over the past five years were: 15%, 13%, -20%, 10% and 18%. The returns on Stock B for the past five years were: -10%, 20%, 30% 15% and -5%. What was the population standard deviation of the portfolio's returns? 8.92% 6.95% 7.97% 7.77%