Marginal Incorporated (MI) has determined that its after-tax cost of debt is 5.0% for the first $74 million in bonds it issues, and 9.0% for any bonds issued above $74 million. Its cost of preferred stock is 13.0%. Its cost of internal equity is 18.0%, and its cost of external equity is 20.0%. Currently, the firm's capital structure has $396 million of debt, $48 million of preferred stock, and $156 million of common equity. The firm's marginal tax rate is 35%. The firm's managers have determined that the firm should have $58 million available from retained earnings for investment purposes next period. What is the firm's marginal cost of capital at a total investment level of $78 million?