i need explanation acct 202

ABC Company uses balance sheet approach to estimate uncollectible accounts. P-jor to adjusting entry at the end of the period, the balances of accounts receivable and allowance for doubtful accounts are $178,000 (debit balance) and $19,900 (credit balance), respectively. At the end of the period, the following aging schedule is prepared: What is the total estimated amount of uncollectible accounts at the end of the period? Select one: a. $10,000 b. $19,900 c. $29,900 d. $19,000