Equipment with a cost of $105,840, an estimated residual value of $5,040, and an estimated life of 14 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. $5,503 b. $9,630 c. $12,840 d. $28,800