A factory machine is purchased for $50,000 on July 1. The machine is expected to have no salvage value at the end of its useful life of 5 years and be useful for 25,000 machine hours. The company decides to use the units-of-production method for depreciating the asset. If the machine is used for 1,920 hours during the first year, what is the net book value of the asset at the end of year one?