please show how you get each journal entry because I am not understanding how to calculate the accumulated depreciation and retained earnings.

In January 2018, installation costs of $6,000 on new machinery were charged to Maintenance and Repairs Expense. Other costs of this machinery of $30,000 were recorded correctly and have been |depreciated (for 2018 and 2019) using the straight-line method with an estimated life of 10 years and no salvage value. During 2020, it is decided that the machinery has a remaining useful life of 20 years, as of January 1, 2020. What entry(ies) should be made in 2020 to correctly record transactions Felated to machinery, assuming the machinery has no salvage value