how to do this question? do show the calculation with formulas on a piece of paper or smth not a excel sheet as I need to do it on a paper

5) WACC and optimal capital structure. 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. Its treasury staff has consulted with investment bankers and, on the basis of those discussions, has created the following table showing its debt cost at different levels: Page 1 of 2 Eiliott uses the CAPM to estimate its cost of common equity, r, 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. Ellioft estimates that if it had no debt, its "unlevered" beta, bu, would be 1.2. What is the firm's optimal capital structure, and what would be its WACC at the optimal capital structure? (11.45\%)