WACC. Thunderhorse Oil is a U.S. oil company. Its current cost of debt is 7%, and the 10 -year U.S. Treasury yield, the proxy for the risk-free rate of interest, is 3%. The expected return on the market portfolio is 8%. The company's effective tax rate is 39%. Its optimal capital structure is 60% debt and 40% equity. A. If Thunderhorse beta is estimated at 1.1 , what is its weighted average cost of capital? B. If Thunderhorse's beta is estimated at 0.8 , significantly lower because of the continuing profit prospects in the global energy sector, what is the company's weighted average cost of capital