Units-of-activity Depreciation A truck acquired at a cost of $335,000 has an estimated residual value of $20,000, has an estimated useful life of 42,000 miles, and was driven 3,400 miles 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 per mile (c) The units-of-activity depreciation for the year