A machine which cost $500,000 is acquired on October 1, 2020. Its estimated salvage value is $50,000 and its expected life is six years. Round all answers to the nearest dollar.

a. Calculate depreciation expense for 2020 and 2021 using the straight-line method.

b. Calculate depreciation expense for 2020 and 2021 using the double-declining balance method.

c. Calculate depreciation expense for 2020 and 2021 using the sum-of-the-years'-digits method.