Thunderhorse Oil. Thunderhorse Oil is a U.S. oil company. Its current cost of debt is 7.60%, and the 10-year U.S. Treasury yield, the proxy for the risk-free rate of interest, is 3.60%. The expected return on the market portfolio is 8.20%. The company's effective tax rate is 39%. Its optimal capital structure is 65% debt and 35% equity a. If Thunderhorse's beta is estimated at 1.50, what is Thunderhorse's weighted average cost of capital? b. f Thunderhorse's beta in estimated at 1.00, significantly lower because of the continuing profite prospects in the global energy sector, what is Thunderhorse's weighted average cost of capital