Mike Conway is a lawyer who requires that his clients pay him in advance of legal services rendered. Mike routinely credits Legal Service Revenue when his clients pay him in advance. In June Mike collected $12,000 in advance fees and completed 75% of the work related to these fees. What adjusting entry is required by Mike's firm at the end of June?

1) Legal Service Revenue 3,000 Unearned Revenue 3,000

2) Unearned Revenue 3,000 Legal Service Revenue 3,000

3) Unearned Revenue 9,000 Legal Service Revenue 9,000

4) Cash 12,000 Legal Service Revenue 12,000

I need an explanation - not just the answer