Martin company purchases a machine at the beginning of the year at a cost of $60,000. The machine is depreciated using the double declining balance method. The machine's useful life is estimated to be 4 years with a $5,000 salvage value. Depreciation expense in year 4 is:

a. $30,000

b. $2,500

c. 13,750

d. $5,000

e. $3,750