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Determine the amount to be added to Allowance for Doubtful Accounts in each of the following cases and indicate the ending balance in each case. a. Credit balance of $500 in Allowance for Doubtful Accounts just prior to adjustment. Using the aging method, the balance of Allowance for Doubtful Accounts is estimated as $8,390. b. Credit balance of $500 in Allowance for Doubtful Accounts just prior to adjustment. Bad debt expense is estimated at 1% of credit sales, whicl totaled $1,139,000 for the year