Please show simple explanation

The ledger of Wainwright Company at the end of the current year shows Accounts Receivable $82,000; Credit Sales $876,000; and Sales Returns and Allowances $51,400. (Credit account titles are automatically indented when amount is entered. Do not indent manually.)

a If Wainwright uses the direct write-off method to account for uncollectible accounts, journalize the adjusting entry at December 31, assuming Wainwright determines that Hiller's $840 balance is uncollectible.

b If Allowance for Doubtful Accounts has a credit balance of $840 in the trial balance, journalize the adjusting entry at December 31, assuming bad debts are expected to be 11% of accounts receivable.

c If Allowance for Doubtful Accounts has a debit balance of $910 in the trial balance, journalize the adjusting entry at December 31, assuming bad debts are expected to be 10% of accounts receivable.