Determine the amount to be ad$$ed to Allowance for Doubtrul Accounts in each of the following rases and indicate the ending balance in each case.

$($a$)$ Credit balance of $$300$ in Allowance for Doubtful Accounts just prior to adjustment. Analysis of Accounts Receivable indicates uncollectible receivables of $$8,500,$

$($b$)$ Credit balance of $$500$ in Allowance for Doubtful Accounts just prior to adjustment. Uncollectible receivables are estimated at $2\%$ of credit sales, which totaled $$1,000,000$ for the year.