Perdue Company purchased equipment on April 1 for $52,320. The equipment was expected to have a useful life of three years, or 7,200 operating hours, and a residual value of $1,920. The equipment was used for 1,300 hours during Year 1, 2,500 hours in Year 2, 2,200 hours in Year 3, and 1,200 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) the units-of-activity method, and (c) the double-declining-balance method.