Company XYZ purchased a building for $2 million cash. The building has a useful life of 40 years and a salvage value of $200,000. Calculate the annual depreciation expense using the sum-of-the-years' digits method and prepare the journal entry to record the depreciation for the first year. Explain the sum-of-the-years' digits method of depreciation and its significance in allocating the cost of long-term assets over their useful lives.