I need the answer for all this 5 question please ?

Q1. What is the Contra Account, explain it( give an example and make a journal entry )? Q2 On July 5, the Advertising Agency paid $300 for office equipment and on July 30, depreciated office equipment for $30. Make journal and ledger entries for depreciation? Q3. On Sep.30 record interest expense for 30 days on 12 percent $ 5.000 promissory note issued August 31 ? Q4. On Dec.31, Management estimated that approximately $6000 of the $100,000 of accounts receivable was uncollectable. Make journal entry for this