Castle Company provides estimates for its uncollectible accounts. The allowance for uncollectible accounts had a credit balance of $18,180 at the beginning of 2021 and a $24,210 credit balance at the end of 2021 (after adjusting entries). If the direct write off method had been used to account for uncollectible accounts (bad debt expense equals actual write-offs), the income statement for 2021 would hove included bad debt expense of $18,900 and revenue of $4,000 from the collection of previously written off bad debts