The balance in the allowance for doubtful account is $30,000 credit. You write off $18,000 on a specific invoice to Bob. Later, Bob pays you $2000 on these written off invoices. At year-end, you estimate that $25,000 of invoices will not be collectible. Make all the appropriate journal entries.

To make the appropriate journal entries, we first need to understand the concept of allowance for doubtful accounts and the accounting treatment for bad debts.

1) The allowance for doubtful accounts is a contra-asset account that represents the estimated amount of accounts receivable that may not be collected. It is used to reduce the accounts receivable to their estimated net realizable value.

2) Bad debts occur when customers are unable to pay their outstanding invoices, and they need to be written off. Writing off a bad debt means removing the uncollectible amount from accounts receivable and the allowance for doubtful accounts.

Based on the information provided, let's break down the journal entries step by step:

1. Initially, the allowance for doubtful accounts balance is $30,000 credit:
Allowance for Doubtful Accounts $30,000
Accounts Receivable $30,000

2. We write off a specific invoice to Bob worth $18,000 from accounts receivable and the allowance for doubtful accounts:
Allowance for Doubtful Accounts $18,000
Accounts Receivable $18,000

3. Bob later pays $2,000 on the written-off invoices, implying a partial recovery of a previously written-off amount. We need to reinstate this amount:
Accounts Receivable $2,000
Allowance for Doubtful Accounts $2,000

4. At year-end, we estimate that $25,000 of invoices will not be collectible. We need to adjust the allowance for doubtful accounts to reflect this estimation:
Bad Debt Expense $25,000
Allowance for Doubtful Accounts $25,000

After making the above journal entries, the revised balance for the allowance for doubtful accounts would be $35,000 credit ($30,000 + $18,000 - $2,000 + $25,000). The bad debt expense will also be recognized in the income statement.