J. Ross and Sons Inc. has a target capital structure that calls for 40 percent debt, 10 percent preferred stock, and 50 percent common equity. Ross' common stock currently sells for $40 per share. The firm recently paid a dividend of $2 per share on its common stock, and investors expect the dividend to grow indefinitely at a constant rate of 10 percent per year. J. Ross's cost of retained earnings is closest to: