Richmond Clinic has obtained the following estimates for its costs 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. Can someone show me step by step how this problem is calculated. I have been using the formula: CCC=[Wdx R(Rd) x (1-T) + [Wex R(Re)] but I'm not sure that I am plugging the right numbers into the equation.