A three-year-old machine has a cost of $29,800, an estimated residual value of $1,800, and an estimated useful iffe of 35,000 machine hours. The company uses units-of-production depreciation and ran the machine 4,600 hours in year 1;6,150 hours in year 2; and 7,400 hours in year 3. Calculate the net book value at the end of the third year