On january 1, year 1, li company purchased an asset that cost $30,000. the asset had an expected useful life of five years and an estimated salvage value of $6000. li uses the straight-line method for the recognition of depreciation expense. at the beginning of the fourth year of usage, the company revised its estimated salvage value to $3000. based on this information, the amount of depreciation expense to be recognized at the end of year 4 is:
a) $12,800.b) $16,800.c) $33,600.d) $20,800.