The calculation for annual depreciation using the double-declining balance method is Oa. a. (Cost - Residual Value) / (1 = Estimated useful life) x 2 b. Initial Cost x (1 + Estimated useful life) x 2 c. (Cost - Residual Value) / (Estimated useful life x 2) Od. Beg. of Year Book Value x (1 Estimated useful life x 2)