Equipment with a cost of $160 000, an estimated residual value of $40 000 and an estimated life of 15 years was depreciated by the straight-line method for 4 years. Due to obsolescence, it was determined that the useful life should be shortened by 3 years and the residual value changed to zero. The depreciation expense for the current and future years is: $11,636 $16,000 $11,028 $18,000