On January 1, Year 1, Dunn Brothers, Inc., purchased a new smartphone case making machine at a cost of $72,000. The estimated residual value was $8,000. Assume that the estimated useful life was four years and the estimated productive life of the machine was 640,000 units. Actual annual production was as follows: Year Units 1 192,000 2 140,800 3 176,000 4 131,200 Required: a. Calculate depreciation expense under the Straight-line method for Years 1 to 4. b. Calculate depreciation expense under the Units-of-production method for Years 1 to 4. c. Complete a depreciation schedule under the Double-declining-balance method.