A certain manufacturing company has a financial policy that for any new equipment, the annual depreciation cost should not exceed 10 percent of the original cost( cost basis) at any time with no salvage value or scrap value at end of its useful life. Determine the service life of service life necessary useful life) if the depreciation method used is: a) straight line method b) sinking fund method at 8 percent cost of money interest per annum of 8 percent c) sum of the year digit method