Concept:The closing balance in a sales ledger control account is the balancing figure obtained after comparing total debits and total credits.Explanation:Total debit entries are:Balance b/f $9,000Add dishonoured cheque $4,000Add credit sales $20,000Total debits =9,000+4,000+20,000=$33,000On the credit side, returns inwards are $3,000.Let the closing balance be x.Then, 3,000+x=33,000So, x=33,000−3,000=$30,000Answer:D. $30,000