On January 1, 2009, Carson Company purchased equipment at a cost of $570,000. The equipment was estimated to have a useful life of five years and a salvage value of $60,000. Carson uses the sum-of-the-years'-digits method of depreciation. What should the accumulated depreciation be at December 31, 2011?
a. $340,000
b. $408,000
c. $456,000
d. $510,000