4. Set up the optimal economic life problem ana- lysed in Example 7.6 as an EXCEL spreadsheet, i.e. explore how optimal economic life varies with the discount rate (set up a table in which the value function is tabulated against alternative economic life values and alternative interest rate values). Do this for both the case where the project is a one-off and the case where there is a replacement chain. Compare and contrast your results for the two cases.