Mystery Co purchased equipment for $25 000. Originally it had an estimated useful life of 4 years and a residual value of $5000. At the beginning of the 4th year of the equipment's life the estimated useful life was extended by a further three years and the residual value was reduced to zero. Mystery Co uses the straight-line method to depreciate its equipment. At the end of year 4, how much depreciation should be recorded for the computer? Select one: O a. $4000 O b. $1 250 O c. $2 500 d. $5 000