Perdue Company purchased equipment on April 1 for $82,620. The equipment was expected to have a useful life of three years, or 5,940 operating hours, and a residual value of $2,430. The equipment was used for 1,100 hours during Year 1, 2,100 hours in Year 2, 1,800 hours in Year 3, and 940 hours in Year 4. Required: Determine the amount of depreciation expense for the years ended December 31, Year 1, Year 2, Year 3, and Year 4, by (a) the straight-line method, (b) units-of-output method, and (c) the double-declining-balance method.