A three-year-old machine has a cost of $44,700, an estimated residual value of $2,700, and an estimated useful ife of 35,000 machine hours. The company uses units-of-production depreciation and ran the machine 4,200 hours in year 1,6,750 hours in year 2, and 6,900 hours in year 3. Calculate the net book value at the end of the third year