At the end of the current year, the accounts receivable account has a debit balance of $1,497,000 and sales for the year total $20,960,000. Determine the amount of the adjusting entry to provide for doubtful accounts under each of the following assumptions:

1. The allowance account before adjustment has a debit balance of $10,200. Bad debt expense is estimated at 1/2 of 1% of sales.
2. The allowance account before adjustment has a debit balance of $10,200. An aging of the accounts in the customer ledger indicates estimated doubtful accounts of $21,880.
3. The allowance account before adjustment has a credit balance of $9,400. Bad debt expense is estimated at 1/4 of 1% of sales.
4. The allowance account before adjustment has a credit balance of $9,400. An aging of the accounts in the customer ledger indicates estimated doubtful accounts of $78,000.