为什么分母不减 cost of capital

问题如下：

Suppose that a business line of a bank has a loan book of USD 100 million. The average interest rate is 10%. The book is funded at a cost of USD 5.5 million. The economic capital against these loans is USD 7.5 million (7.5% of the loan value) and is invested in low risk securities earning 5.5% per annum. Operating costs are USD 1.5 million per annum and the expected loss on this portfolio is assumed to be 1% per annum (i.e., USD 1 million). The firm's cost of capital is 15%.The RAROC for this business line is:

选项：

A.26.70% B.37.10% C.21.20% D.32.20%

解释：

The RAROC for this business line is: Risk-adjusted return / Risk-adjusted capital = (100 × 0.1 - 5.5 - 1.5 - 1 + 7.5 × 0.055）/7.5 = 2.4125 / 7.5 = 32.2%