Williams company purchased a machine costing $29,400 and is depreciating it over a 10-year estimated useful life with a residual value of $3,400. at the beginning of the eighth year, a major overhaul on it was completed at a cost of $8,400, and the total estimated useful life was changed to 12 years with the residual value unchanged. how much is the year 8 depreciation expense assuming use of the straight-line depreciation method?