4. Mai purchased equipment on January 1, 2019, at a cost of $60,000. At the time of purchase, the equipment was expected to have a five-year economic life and a residual value of $5,000. Mai uses straight-line depreciation. At December 31, 2021 (year 2021 was not calculated yet), Mai estimated the equipment to have a remaining life of three years with no residual value. For the year ended December 31, 2021, Mai would report depreciation expense of