Equipment with a cost of $70,505, an estimated residual value of $6,787, and an estimated life of 15 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. $3,284.38 b. $8,210.94 c. $21,239.33 d. $5,473.96