Thunderhorse Oil. Thunderhorse Oil is a U.S. oil company. Its current cost of debt is 7.20%, and the 10 -year U.S. Treasury yield, the proxy for the risk-free rate of interest, is 4.00%. The expected return on the market portfolio is 8.50%. The company's effective tax rate is 39%. Its optimal capital structure is 75% debt and 25% equity. a. If Thunderhorse's beta is estimated at 1.60 , what is Thunderhorse's weighted average cost of capital? b. If Thunderhorse's beta is estimated at 1.10 , significantly lower because of the continuing profit prospects in the global energy sector, what is Thunderhorse's weighted average cost of capital? a. If Thunderhorse's beta is estimated at 1.60 , what is Thunderhorse's weighted average cost of capital? \% (Round to two decimal places.) b. If Thunderhorse's beta is estimated at 1.10 , significantly lower because of the continuing profit prospects in the global energy sector, what is Thunderhorse's weighted average cost of capital? \% (Round to two decimal places.)