Nula’s accounting year finishes on 31 December. She keeps a provision for doubtful debts equal to $5\%$ of trade receivables. At 1 January 2021, the provision was $800$. By 31 December 2021, trade receivables totalled $13400$, and $600$ of this was considered irrecoverable. What amount was shown for the provision for doubtful debts at 1 January 2022?
- A$600$
- B$640$
- C$660$
- D$670$