Company Audi's capital structure includes Equity, Preference shares and Bonds (Debt). It wants to calculate its WACC (Weighted average cost of capital) Capital Structure: The market value of Audi's equity, preferred stock, and debt are $ 7 billion, $ 3 billion, and $ 14 billion, respectively. Equity and Beta Details: Audi has a beta of 1.8, the market risk premium is 9%, and the risk-free rate of interest is 4%. Preference Share: Audi's preferred stock pays a dividend of $ 5 each year and trades at a price of $ 31 per share. Debt: Audi's debt trades with a yield to maturity of 9.0%. 

Calculate Audi's weighted average cost of capital if its tax rate is 40%.