On March 31, 2018, Canseco Plumbing Fixtures purchased equipment for $48,000. Residual value at the end of an estimated four-year service life is expected to be $6,000. The company expects the machine to operate for 12,000 hours. a. Calculate depreciation expense for 2018 and 2019 using straight line method. b. Calculate depreciation expense for 2018 and 2019 using sum-of-the-years-digits method. c. Calculate depreciation expense for 2018 and 2019 using double-declining balance method.