Machinery acquired new on January 1 at a cost of $70,000 was estimated to have a useful life of 9 years and a residual salvage value of $7,000. Straight-line depreciation was used. On January 1, following six full years of use of the machinery, management decided that the estimate of useful life had been too long and that the machinery would have to be retired after two years, that is, at the end of the eighth year of service. Under this revised estimate, the depreciation expense for the seventh year of use would be:

$10,500.

$21,000.

$10,500.

$7,000.