Nula’s financial year finishes on 31 December. She keeps a provision for doubtful debts equal to $5\%$ of trade receivables. On 1 January 2021, the provision stood at $800. By 31 December 2021, trade receivables were $13\,400$, and $600$ of this amount was considered irrecoverable. What amount was shown for the provision for doubtful debts on 1 January 2022?
- A$600
- B$640
- C$660
- D$670