Drake Corporation bought a machine at the beginning of the year at a cost of $50,000. The estimated useful life was five years and the residual value was $5,000. Assume that the estimated productive life of the machine is 10,000 units. Expected annual production for year 1 is 3,000 units; year 2 is 2,000 units; year 3 is 1,800 units; year4 is 1,700 its;and year 5 is 1,500 units. What is the Book Value of the machine at the end of year 4 under the double-declining-balance method? $1,480 $1,912 $6.912 O$6,480