Concept:Useful life is the number of years an asset can be used, calculated by dividing total depreciation by annual depreciation.Explanation:From the table, the cost price is N20,000.The salvage value is N5,000.The annual depreciation is N1,000.Total depreciation =Cost price−Salvage value.Total depreciation =20,000−5,000=15,000.Useful life =Annual depreciationTotal depreciation.Useful life =1,00015,000=15 years.Therefore, Y=15 years.Answer:Option C. 15 years.