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A three-year-old machine has a cost of $21,800, an estimated residual value of $1,400, and an estimated useful life of 34,000 machine hours. The company uses units-of-production depreciation and ran the machine 3,600 hours in year 1; 7,450 hours in year 2; and 6,700 hours in year 3. Calculate the net book value at the end of the third year. et book value