Elliott Athletics is trying to determine its optimal capital structure, which now consists of only debt and common equity. The firm does not currently use preferred stock in its capital structure, and it does not plan to do so in the future. To estimate how much its debt would cost different debt levels, the company's treasury staff has consulted with investment bankers and on the basis of those discussions, has created the following table: Elliott uses the CAPM to estimate its cost of common equity, k. The company estimates that the risk-free rate is 5 percent, the market risk premium is 6 percent, and its tax rate is 40 percent. Elliott estimates that if it had no debt, its "unlevered" beta, b_U, would be 1.2. On the basis of this information, what is the firm's optimal capital structure, and what would be the weighted average cost of capital at the optimal capital structure