Final answer:
The net book value of the machine is $8,000, calculated by subtracting the accumulated depreciation of $4,000 from the original cost of $12,000.
Step-by-step explanation:
The net book value of a machine is calculated by subtracting the accumulated depreciation from the original cost of the machine. In this scenario, the original cost of the machine is $12,000 and the accumulated depreciation is $4,000. Therefore, the net book value would be:
$12,000 (Original Cost) - $4,000 (Accumulated Depreciation) = $8,000 (Net Book Value)
The current market value of the machine, which is $7,000 in this case, does not affect the calculation of net book value.