Purity Ice Cream Company bought a new ice cream maker at the beginning of the year at a cost of $20,000. The estimated useful life was four years, and the residual value was $2,180. Assume that the estimated productive life of the machine was 9,900 hours. Actual annual usage was 3,960 hours in year 1; 2,970 hours in year 2; 1,980 hours in year 3; and 990 hours in year 4.

Year	Depreciation expense	Accumulated depreciation	Netbook value
At acquisition			20,000
1	10,000	10,000	10,000
2	5000	15000	5000
3	2500	17500	2500
4	??	???	???