Commercial Construction Builders has a beta of 1.34, a dividend growth rate of 2.1 percent for the foreseeable future, a stock price of $15 per share, and an expected annual dividend of $0.45 per share next year. The market rate of return is 12.8 percent and the risk-free rate is 4.2 percent. What is the firm's average cost of equity? Please explain with full formula.