I need help with this problem... plz add equations and functions so I can understand how you got the answer, real appreciated!

PROBLEM SET 4 Chapter 9 Cost of Capital Assigned Problem 1 Richmond Clinic has obtained the following estimates for its costs of debt and equity at various capital structures: After-Tar Percent Cost of Cost of Equity Debt Debt 0% 16% 20% 6.6% 17% 40% 7.8% 60% 10.2% 22% 27% 80% 14.0% 8 Using this information, what should be the firm's optimal capital structure? (Hint: Calculate the corporate cost of capital at each structure. Note that the costs of debt given in this problem are after-tax costs. Also, note that data on component costs at alternative capital structures are not 2 reliable in real-world situations.) 3