The historical returns on a portfolio had an average return of 19% and a standard deviation of 12%. Assume returns on the portfolio follow a bell-shaped distribution. Use the empirical rule to answer the following questions. a. What percentage of returns were between 7 percent and 31 percent? Percentage of returns % b. What percentage of returns were greater than 31 percent? Percentage of returns % c. What percentage of returns were below -5 percent? Percentage of returns %