现在的情况是no borrowing, 所以没有利息可以用来免税，所以EBT = EBIT = 250m
Asset = Equity + Debt: 2500m = 2500m + 0m
Tax = EBT x Tax rate: 250m x 25.5% = 63.75m

如果现在公司借钱融资：Ｄ，那么EBT = EBIT - Interest = 250m - (D x 6%)
Asset = Equity + Debt: 2500m = 2500m-D + D
1. Tax = EBT x Tax rate: [250m - (D x 6%)] x 25.5%
2. Tax = EBIT x Effective Tax Rate: 250m x 22% = 55m

Therefore combining 1 & 2
[250m - (D x 6%)] x 25.5% = 55m
D= 571.9m ==>需要借571.9m
Equity= 2500m-D= 1928.1m

Note:以上是基于题目的条件给出的解答，但是我觉得这个题目出的有点问题，因为Effective Tax Rate应该也是Tax/EBT，而不是等式2里面的Tax = EBIT x Effective Tax Rate. 但是根据这个严格的定义，此题就无解了。　

假如我用 EBIT/6% 得出 EBIT 的PV 4166.67 million，
tax payment 1 = tax rate1* (pv)ebit= 25.5%*4166.67=1062.5
tax payment 2= tax rate2* (pv)ebit=22%*4166.67=916.67
税盾ITS = 145.83 debt=662.86 这么算有什么问题吗 为什么会有两个结果

虽然你加了永久折现率的概念，但本质上你的前两个等式和我的是一样的：
你的tax payment 1就是我的63.75m/6%,你的tax payment 2就是我的55m/6%
你我不同的地方在于你的最后一步从税盾到Debt是怎么算出来的：我用的税率是25.5%，而你用了22%。
我的税盾是63.75m-55m=8.75m per year, Debt= 8.75m/25.5%/6%=571.9m
你的税盾是 63.75m/6%-55m/6%=145.83m, Debt= 145.83m/22%= 662.86m