請問一題關於壞帳的問題 - 會計

題目是這樣寫的：
Assume that Hively Company decides to
estimate its bad debts expense based of 5% of accounts receivable.
What amount of bad debts expense will Hively Company record if
Allowance for Doubtful Accounts has a credit balance of $4,000?
這題的答案是
(A/R的金額*5%)-$4,000
我想請問為什麼不是先把A/R的金額減掉4,000再乘上5%???
因為Allowance for Doubtful Accounts有餘款表示壞帳費用其實沒那麼多，
那把Allowance for Doubtful Accounts勾銷的時候不是要貸A/R嗎？
然後再把剩下的A/R*5%?
我不太清楚這題解法的意思
謝謝

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