Takeoka's Sushi To Go has estimated the following cost of debt (before-tax) and cost of equity. Proportion of Debt || Before-tax Cost of Debt || Cost of Equity 30% || 9.5% || 14.4% 40% || 9.7% || 15.2% 50% || 10.1% || 16.2% 60%||11.8%||18.5% What is the cost of capital at Takeoka's optimal capital structure given the above information and a 40% effective tax rate?