Perdue Company purchased equipment on April 1 for $54,270. The equipment was expected to have a useful life of three years, or 7,020 operating hours, and a residual value of $1,620. The equipment was used for 1,300 hours during Year 1, 2,500 hours in Year 2, 2,100 hours in Year 3, and 1,120 hours in Year 4. 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) the units-of-activity method, and (c) the double-declining-balance method.