Allowance for Doubtful Accounts has a debit balance of $500 at the end of the year, before adjustment, and uncollectible accounts expense is estimated at 3% of net sales. If net sales are $600,000, the amount of the adjusting entry to record the provision for doubtful accounts is: a. $12,000 b. $6,800 c. $18,000 d. $1,800