In order to convert the average annual net cash inflow from the asset back to the average annual operating income from the asset

If you know the average annual net cash flow and you want to know the average annual operating income, you must look for the annual depreciation expense and subtract it from the net cash flow.

The formula for calculating net cash flows = operating income + depreciation expense

therefore,

operating income = net cash flows - deprecation expense

explanation:

the contractual interest rate is the interest the borrower must pay and the interest the lender receives, or more simply, it is the interest rate stated on a bond whereas the market interest rate is “the investors demand for loaning funds”. therefore, bonds can either be sold at a premium, face value, or discount.