Takeoka's Sushi To Go has estimated the following cost of debt (before-tax) and cost of equity.
Proportion of DebtBefore-tax Cost of DebtCost 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?