At the end of the current year, the accounts receivable account has a debit balance of $2,700,000 and sales for the year total $32,400,000. Determine the amount of the adjusting entry to provide for doubtful accounts under each of the following assumptions:

a. The allowance account before adjustment has a debit balance of $27,100. Bad debt expense is estimated at ½ of 1% of sales.

b. The allowance account before adjustment has a debit balance of $27,000. An aging of the accounts in the customer ledger indicates estimated doubtful accounts of $128,000. 

c. The allowance account before adjustment has a credit balance of $17,900. Bad debt expense is estimated at ¾ of 1% of sales.

d. The allowance account before adjustment has a credit balance of $17,900. An aging of the accounts in the customer ledger indicates estimated doubtful accounts of $279,000.