Castle Rock owns a machine that it purchased on January 1, 2013 for $400,000. The machine had an estimated useful life of 10 years with a production capacity for 80,000 units. The company uses the units-of-production method to record depreciation. The machine produced 15,000 units in 2013, 18,000 units in 2014 and 25,000 units in 2015. What was the depreciation expense for 2015?