Cost Price (N) = 20000 Salvage value (N) = 5000 Annual depreciation (N) = 1000 Total depreciation = 15000 The formula to calculate the useful life is: Useful life = (Cost Price - Salvage value) / Annual depreciation Now, let's plug in the values: Useful life = (20000 - 5000) / 1000 Useful life = 15000 / 1000 Useful life = 15 years Therefore, the useful life represented by Y in the table is 15 years.