Please show work. The answer is 11.90% but I do not understand how. Thanks

Allison Engines Corporation has established a target capital structure of 40 percent debt and 60 percent common equity. The current market price of the firm's stock is PO = $59.6; its next dividend will be D1 = $3.4, and its expected dividend growth rate is 6.2 percent. What will 71 Allison's marginal cost of retained earnings, rs, be? 72