A machine that cost $144,000 has an estimated residual value of $12,000 and an estimated useful life of 12,000 machine hours. The company uses units-of-production depreciation and ran the machine 2,000 hours in year 1, 3,000 hours in year 2, and 4,000 hours in year 3. Calculate its book value at the end of year 3. (Do not round intermediate calculations.)