Equipment with a cost of $89,752, an estimated residual value of $6,499, and an estimated life of 13 years was depreciated by the straight-line method for 4 years. Due to obsolescence, it was determined that the remaining useful life should be shortened by 4 years and the residual value changed to zero. The depreciation expense for the current and future years is a. $25,616.31 b. $12,827.14 c. $4,933.51 d. $8,016.96