Depreciation is the systematic allocation of the cost of an asset to the income statement over the estimated useful life of that asset.
It is determined as the depreciable value of the asset over the estimated useful life of the asset where the depreciable value is the difference between the cost and salvage value of the asset
Mathematically,
Depreciation = (Cost - Salvage value)/Estimated useful life
The answer is 35 because if you do 30 over 100 it will be 0.3 so then you are going to take the 10.50 and divide that to 0.3 and that's how you get your answer your answer is going to be 35