A plant asset was purchased on January 1 for $73750 with an estimated salvage value of $10000 at the end of its useful life. The current year's depreciation expense is $4250 calculated on the straight-line basis and the balance of the Accumulated Depreciation account at the end of the year is $21250. The remaining useful life of the plant asset is

10 years. 17.4 years. 20 years. 12.4 years.