On 1 January 2019, Don Company purchased a machine for $100,000. The machine was estimated to have a useful life of 5 years with no residual value. On 1 January 2021, the company determined that, due to advances in machinery maintenance, the total useful life of the machine would be 7 years. On 1 January 2022, the company traded in the machine and paid $20,000 for a new machine. There was no gain or loss on the exchange of the machine. The company uses the straight-line method of depreciation and the company's financial year ends on 31 December. (a) Compute the depreciation expense, accumulated depreciation and net book value of the machine for each of the years 2019,2020 and 2021. Show workings. (12 marks) (b) Present journal entries to record the trade-in of the old machine for the new machine. (5 marks) (c) Explain the concept of depreciation and why it requires the use of judgement and estimates. (8 marks)