b. Silver Co. acquired a machine on April 1, 2020, at a cost of $54,600. The machine has an estimated salvage value of $ 4,200 at the end of its 7-year useful life. The depreciation adjustment is done at the end of every calendar year. Depreciation expense Depreciation expense Book value as of Depreciation method for 2020 for 2021 Dec. 31, 2021 1 Sum-of-the-years-digits Double declining balance