please provide an explanation for part A as well I got the answer right for part B but please explain why

Kingbird, Inc. uses the percentage-of-receivables basis to record bad debt expense. Accounts receivable (ending balance) $629,000 (debit) Allowance for doubtful accounts (unadjusted) 3,800 (debit) The company estimates that 2% of accounts receivable will become uncollectible. (a) Your answer is correct. Prepare the adjusting journal entry to record bad debt expense for the year. (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 0 for the amounts.) Account Titles and Explanation Debit Credit Bad Debt Expense 16380 Allowance for Doubtful Accounts 16380 (b) Your answer is partially correct. What is the ending (adjusted) balance in Allowance for Doubtful Accounts? (Post entries in the order of journal entries posted in the previous part) Allowance for Doubtful Accounts Unadj. Bal. A 3800 Bad Debts 16380 Adj. Bal. 20180 eTextbook and Media List of Accounts