A machine with an original cost of $120,000 and no salvage value had an estimated useful life of 6 years, but after 4 complete years, it was decided that the original estimate of useful life should have been 8 years. Assuming the company uses straight-line depreciation, the amount of depreciation expense in year 5 is

a) 20,000
b) 80,000
c) 10,000
d) 12,000
e) 5,000