Sarah has just purchased a new machine which she expects to use for 4,000 hours over the next five years. The machine cost $42,000 and is expected to have a salvage value of $2,000 at the end of its useful life. Sarah used the machine for 600 hours in the first year. Assuming she uses the double-declining-balance method, the machine's accumulated depreciation at the start of year 2 15: Select one: a $16,800 b. None of these c. $8,400 O d. $4,000