Answer:
Allowance for doubtful accounts Dr $12,800
Accounts receivables Cr $12,800
(To record amount written off)
Accounts receivables Dr $3,000
Allowance for doubtful accounts Cr $3,000
(To reverse writeoff)
Cash Dr $3,000
Accounts receivables Cr $3,000
(To record collection of writeoff)
Bad debt expenses Dr $25,000
Allowance for doubtful accounts Cr $25,000
Workings:
Balance before adjustment in Allowance $5,600
for doubtful accounts (15,400-12,800+3,000)
Less: Required amount $30,000
Additional provision required $25,000