In 2011, Davis Company had net sales of $750,000. On January 1, 2011, Allowance for undoubtful accounts had a credit balance of $18,000. During 2011, $30,000 of uncollectible accounts receivable were written off. Past experience indicates that 3% of net credit sales become uncollectible. What should be the adjusted balance of allowance for doubtful accounts at December 31,2011?