A three-year-old machine has a cost of $43,900, an estimated residual value of $1,000, and an estimated useful life of 33,000 machine hours. The company uses units-of-production depreciation and ran the machine 4,500 hours in year 1; 7,150 hours in year 2; and 8,100 hours in year 3. Calculate the net book value at the end of the third year. Net book value