Two years ago, a company issued $20 million in long-term bonds at par value with a coupon rate of 9 percent. The company has decided to issue an addi- tional $20 million in bonds and expects the new issue to be priced at par value with a coupon rate of 7 percent. The company has no other debt outstanding and has a tax rate of 40 percent. To compute the company's weighted average cost of capital, the appropriate after-tax cost of debt is closest to:

   答案是 4.2%.  是直接用7%*0.6

   我想请问的是 第一句话难道没有用么？  为什么成本不是 先求7%+9%的加权平均 即8%  然后再乘以（1-t）？即答案是4.8%

                                                                                    谢谢各位大神了！！