Final answer:
The increasing depreciation-to-cost ratio at Hercules Inc. most likely occurs because the machinery's estimated useful life is set longer than its actual useful life, leading to a higher accumulated depreciation. Option B is correct answer.
Step-by-step explanation:
The increasing ratio of total accumulated depreciation to the total cost of machinery could result from the estimated average useful life of Hercules Inc.'s machinery being greater than its actual average useful life. This means that Hercules Inc. depreciates its machinery over a longer period than it actually should, resulting in a yearly increase in the depreciation expense without a corresponding increase in the investment in new machinery. As the older equipment continues to be used without adequate replacement, the proportion of accumulated depreciation to total cost grows, hence the ratio becomes steeper over time.