Computing Depreciation Expense for Change in Useful Life Phelps Company purchases equipment on January 1, 2019, for $50,400 which will be depreciated using the sum of years' digits method. The equipment has a residual value of $8,400 and a useful life of three years. In 2020, Phelps decides that the machine has an original total useful life of four years and $4,200 salvage value. What is depreciation expense for 2020 Depreciation expense for 2020 s