Company STU purchased equipment for $400,000 cash. The equipment has a useful life of 8 years and a salvage value of $40,000. 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.