In 2001 Rachel Fisher Co. had net credit sales of $750,000. On January 1, 2001, allowance for doubtful accounts had a credit balance of $18,000. During 2001, $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, 2001?