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A company purchased machinery that cost $510,000. It has a 8 year estimated useful life. It is estimated that the machine will be operated for 100,000 hours over its useful life and have a salvage value of $10,000. If the machine had been operated for 22,000 hours for year 3 . Calculate depreciation expense under 1) straight-line method. 2) unit-of-production method. 3) double-dec ining balance method