Answer both questions completely

Is it necessary for a business to use the same method of computing depreciation: for all classes of its depreciable assets, for financial statement purposes and in determining income taxes? For some of the fixed assets of a business, the balance in Accumulated Depreciation is exactly equal to the cost of the asset. Is it permissible to record additional depreciation on the assets if they are still useful to the business and currently used in operation? When should an entry be made to remove the cost and the accumulated depreciation from the books