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A tractor acquired at a cost of $420,000 has an estimated residual value of $30,000, has an estimated useful nfe of 25,000 hours, and was operated 1,850 hours. during the year. Determine the following. If required, round your answer for the depreciation rate to two decimal places. (a) The depreciable cost (b) The depreciation rate (c) The units-of-activity depreciation for the year