A machine cost $1,218,000 on April 1,2020. its estimated salvage bakue is 145,200 and ite expected life is 4 years. a) calculate the depreciation expense by straight line foe 2020. b) calculate the depreciation expense by double-declining balance of 2021. c) calculate the depreciation expense by sum of the years digits for 2021. d) which method would result in the smallest income fir 2021