Final answer:
The depreciation expense for 2013 using the straight-line method would be $71,428. The correct option is D.
Step-by-step explanation:
To calculate the depreciation expense for 2013 using the straight-line method, we need to determine the remaining useful life of the machinery.
Since the machinery was initially expected to have a useful life of 10 years and it was already in use for 3 years at the beginning of 2013, the remaining useful life is 7 years (10 - 3 = 7).
To calculate the depreciation expense using the straight-line method, we divide the cost of the machinery ($500,000) by its remaining useful life (7 years): $500,000 / 7 = $71,428. Therefore, the correct answer is option d: $71,428.