Equipment with a cost of $88,200, an estimated residual value of $4,200, and an estimated life of 14 years was depreciated by the straight-line method for 5 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 $30,000 b. $4,157 c. $11,640 d. $6,467