C&C Company purchased a minicomputer on January 1, 2016, at a cost of $60,000. The computer was depreciated using the sum-of-the-years-digits method over an estimated eight-year life with an estimated residual value of $2,400. On January 1, 2018, the estimate of useful life was changed to a total of six years, and the estimate of residual value was changed to $1,000. What is the amount of depreciation expense for year 2018?