Concord Co. uses the percentage-of-receivables basis to record bad debt expense and concludes that 4% of accounts receivable will become uncollectible. Accounts receivable are $421,300 at the end of the year, and the allowance for doubtful accounts has a credit balance of $2,921. (a) Prepare the adjusting journal entry to record bad debt expense for the year. (b) If the allowance for doubtful accounts had a debit balance of $870 instead of a credit balance of $2,921, prepare the adjusting journal entry for bad debt expense. (List all debit entries before credit entries. Credit account titles are automatically indented when amount is entered. Do not indent manually. If no entry is required, select "No Entry" for the account titles and enter O for the amounts.)