Answer: This question is incomplete. There should be information on the opening balance and closing balance of allowance for bad debt. See below guidance to solve the question.
Explanation: Typically, account receivable is shown as net of allowance for bad debt. In the question above, there would be an opening balance (for preceding year) and closing balance (for current year) of the allowance for bad debt.
If the information above are present, the movement schedule will be: opening balance + bad debt expense - bad debt written off = closing balance.
To get the bad debt written off, you need to change the subject of the formula and rewrite the equation as: opening balance + bad debt expense - closing balance = bad debt written off. Substituting with those figures would give you the bad debts written off amount required.