provide all calculation with explanation of each + formulas

Elliott is trying to determine its optimal capital structure. The company's capital structure consists of debt and common stock. The company's investment bankers have given the following estimates for Rd. Percent financed Bond rating Before tax cost of debt 7.0% 8.0% | AA with debt 0.00 0.20 0.40 0.60 0.80 A 10.0% 12.0% BBB BB 15.0% Company uses CAPM to estimate it's cost of equity. The risk free rate is 5% and the market risk premium is 6%. Elliott estimates that if it had no debt, it's beta would be 1.2. Company's tax rate is 40% and growth rate is zero. The company estimates its free cash flow to be 30 mn On the basis this information, what is the company's optimal capital structure and what is the firm's cost of capital at this optimal capital structure