You need to estimate the value of Laputa Aviation. You have the following forecasts (in millions of dollars) of its profits and of its future investments in new plant and working capital: From year 5 onward, EBITDA, depreciation, and investment are expected to remain unchanged at year-4 levels(从第5年开始,EBITDA、折旧和投资预期保持第4年的水平不变.). Laputa is financed 50% by equity and 50% by debt. Its cost of equity is 15%, its debt yields 7%, and it pays corporate tax at 40%. a. What is the WACC? b. Estimate the company's total value.(说明第1-4年的FCF、第4年的期末价值、公司价值)