Answer: C-$24,000
Explanation:The units of production method is a method of depreciation where depreciation expense allocated in a year corresponds to the actual use of the asset.
Units of production method = [(Original cost of the machine - salvage value)÷ estimated productive capacity of the machinery] × actual units produced.
The cost of the equipment- $180,000
Salvage value = $ 20,000
Estimated productive capacity- 40,000
Actual production in year 2 - 6000 units
Depreciation expense in year 2 = ( 180000 - 20,000) ÷ 40,000 = $ 4
4 × 6000= $24,000