Question:

Apt complex received 15000 on sept 1 2009 for one years rent in advance and recorded the transaction with a credit to unearned rent. So on December 2007 would I adjust by:

Debit rent revenue and credit unearned rent $10000

Maybe I'm wrong , but I'm kind of confused with the question, On September 2009 APT complex received 15000$ in advance for 1 year Unearned Rent revenue.
... Cash... 15000
... unearned rent revenue... 15000

But, how come APT Complex already earned 10000 $ on Dec 2007 which means 2 years before they received 15000 of unearned rent revenue??

I'm going to guess that one of the two is a typo, either by the OP or whoever put the problem together.

neversatysfyd, couple of things. First, let's just assume those were both 2007 or 2009 and not the way you typed it. If someone paid you in advance for one year, how much of it have you earned from Sept 1 to the end of Dec? That is, how many months. And if it's 15,000 for an entire year that was paid in advance, how much for that many months? ($10,000 is 2/3 of a year's worth, but Sept - Dec isn't 2/3 of a year.)

Also, revenues are always credits. And if you credit the unearned rent, you've added more to it. If you've now earned it, do you have more unearned rent?