Myster Co purchased equipments for $25000. Originally it had estimated useful life of 4 years and a residual value of $5000. At the beginning of the fourth year of the equipments life, the estimated useful life was extended by a further three years and the residual value was reduced to zero. Myster 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?