On March 31, 2021, Canseco Plumbing Fixtures purchased equipment for $40,000. Residual value at the end of an estimated four-year service life is expected to be $4,000. The company expects the equipment to operate for 20,000 hours. The equipment operated for 2,700 and 3,500 hours in 2021 and 2022, respectively. Required: a. Calculate depreciation expense for 2021 and 2022 using straight-line method. b. Calculate depreciation expense for 2021 and 2022 using double-declining-balance method. c. Calculate depreciation expense for 2021 and 2022 using units-of-production using hours operated.