I don't understand Problem 7-1 number 2 letter b). Uncollectible accounts of 18.360 would debit allowance for doubtful accounts and credit accounts receivable. Plus 4.000 minus 2.350 gives 20.010 in debit allowance for doubtful accounts. But the answer shows it's credited. I have a confusion.

b) 'Date Account Title Debit Credit Dec 31 2016 Bad Debt Expenses 20, 010 Allowance for Doubtful Accounts 20, 010