Internal rate of return method The internal rate of return method is used by Testerman Construction Co. in analyzing a capital expenditure proposal that involves an investment of $132,620 and annual net cash flows of $36,000 for each of the six years of its useful life. This information has been collected in the Microsoft Excel Online file. Open the spreadsheet, perform the required analysis, and input your answers in the question below. Open spreadsheet Determine the internal rate of return for the proposal