Perdue Company purchased equipment on April 1 for $55,620. The equipment was expected to have a useful life of 3 years, or 5,400 operating hours, and a residual value of $1,620. The equipment was used for 1,000 hours during Year 1, 1,900 hours in Year 2, 1,600 hours in Year 3, and 900 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.