ARTO Equipment with a cost of $132,300, an estimated residual value of $6,300, 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 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 Oa. $12,338 Ob. $6,580 Oc. $14,100 Od. $33,600