Company Exxon Mobil Corporation purchased equipment for $25 million cash. The equipment has a useful life of 10 years and a salvage value of $3 million. Calculate the annual depreciation expense using the units-of-production method and prepare the journal entry to record the depreciation for the first year. Explain the units-of-production method of depreciation and its significance in allocating the cost of long-term assets based on their usage.