Equipment with a cost of $82,320, an estimated residual value of $3,920, and an estimated life of 14 years was depreciated by the straight-line method for 6 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 Oo. 54872 Ob 533.600 Oc. $12.180 Od. 53.480