Can anyone help me on how to figure out this problem?
Richmond Clinic has obtained the following estimates for its cost of debt and equity at various capital structures:
Percent Debt After-Tax Cost of Debt Cost of Equity
0% ---- 16%

20 6.6% 17
40 7.8 19
60 10.2 22
80 14.0 27
What is the firm’s optimal capital structure? (Hint: Calculate its corporate cost of capital at each structure. Also, note that data on component costs at alternative capital structures are not reliable in real-world situations.)

Question

Can anyone help me on how to figure out this problem?
Richmond Clinic has obtained the following estimates for its cost of debt and equity at various capital structures:
Percent Debt		After-Tax Cost of Debt		Cost of Equity         
       0%			----				16%

20				6.6%			17
      40		 		7.8			19
      60				10.2			22   
   80				14.0			27
What is the firm’s optimal capital structure? (Hint: Calculate its corporate cost of capital at each structure. Also, note that data on component costs at alternative capital structures are not reliable in real-world situations.)