Answer:
At the end of period the allowance for uncollectible debts will be: 15000-3000 = $ 12000 because 3000 account receivable is written off.
Explanation:
(Opening) Allowance for uncollectible accounts = 3000 (Dr)
During the year company estimates = $ 15000
Entry : Dr  Bad debts expense  15000
           Cr Allowance for bad debts   15000
      ( To record uncollectible accounts)