Porter plumbing's stock had a required return of 11.75% last year, when the risk-free rate was 5.50% 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.) select one: a. 14.38% b. 14.74% c. 15.11% d. 15.49% e. 15.87%