Fortune Co. receives $30,000 cash in advance for four months of legal services on October 1, 2011, and records it by debiting Cash and crediting Unearned Revenue, both for $30,000. It is now December 31, 2011, and Fortune has provided legal services as planned. What adjusting entry should Fortune make to account for the work performed from October 1 through December 31, 2011?

You need to calculate the earnings that is earned, then the journal entry will be: debit Unearned Revenue for the amount earned and Credit Service Revenue(or Legal Services Revenue) for the amount.