On January 1, 2015, 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 $6,000. 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 $3,000. Based on this information, the amount of depreciation expense to be recognized at the end of 2018 is:

$6,300.

$4,800.

$12,600.

$7,800.