Porter Plumbing's stock had a required return of 11.75% last year, when the risk-free rate was 7.50% and the market risk premium was 4.75%. Then an increase in investor risk aversion caused the market risk premium to rise by 2%. The risk-free rate and the firm's beta remain unchanged. What is the company's new required rate of return? (Hint: First calculate the beta, then find the required return.) a. 13.07% b. 14.38% c. 13.54% d. 15.87% e. 15.70%