B&B Company purchased a minicomputer on January 1, 2015, at a cost of $50,000. The computer was depreciated using the sum-of-the-years-digits method over an estimated eight-year life with an estimated residual value of $3,200. On January 1, 2017, 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 2017?

a. $14,400 b. $12,500 c. $11,800 d. $10,400