McMullen Company purchased tool sharpening equipment on May 1 for $162,000. The equipment was expected to have a useful life of three years, or 12,000 operating hours, and a residual value of $3,600. The equipment was used for 2,400 hours during Year 1, 3,900 hours in Year 2, 4,050 hours in Year 3, and 1,650 hours in Year 4.

Instructions
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.