basically I'm going to cut it down to the necessary accounts

we are given tehe unadjusted trial balance and we are required to create the adjusted trial balance. However, I am confused with the adjustments:

Other information: inventory, March 31/ 2009----30,000 (is this closing stock?)

given that the unadjusted trial balance figures at march 31/09 were:

inventory 01/04/08: 42,000

How do I adjust these?
first of all, the 'contra?' accounts that I used, like the additional entries included I nthe trial balance from this adjustment were: Closing stock (is this right or is it COGS?)

What I did: (my adjusted trial balance)
1/4/08 invntory = 30,000 Dr ( 42000 - 12,000)--since 30,000 was the final figure found at the end, I credited the difference (12000) from the 42000Dr
THEN:
closing stock or COGS?? : I Dr 12000? ( or do I Debit 30,000)

Is COGS included in the trial balance? Like is there a heading called COGS?

The adjusting entry you need to do for inventory is:
Debit COGS for the amount
Credit Invnetory for the amount.

Your problem states what the actual ending inventory is. It is 30,000
The amount in your inventory account is 42,000
You need to do an adjusting entry to get your inventory account from the 42,000 that is in the account to the actual inventory of 30,000
The adjusting entry will be the difference of 42,000 - 30,000

The trial balance is a listing of all your accounts debit and credit balances. It is used to verify that your Debits = your Credits.
Therefore all of your balance sheet accounts as well as your income statement acocunts will be listed.