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's 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. What is the firm's cost of common stock, rs ? \begin{tabular}{|c} \hline 12.5% \\ \hline 16.5% \\ \hline 10.0% \\ \hline 18.0% \\ \hline 15.5% \\ \hline \end{tabular}