here it is:
In the question you have given you don't need to subtract bad debts from debtor in the balance sheet this is because the bad debts is not written in the additional information which means the effect of the bad debt is already taken on the debtor so you don't need to subtract it from debtor in the balance sheet.
For example in the question below 'Debts of $200
were to be written off' is in Additional information at 30 April 2008 which means the debtor amount($9 000) showed in
30 April 2008 balances is before the bad has been written off from the the debtor amount,so in this question you must subtract $200 from $9000 in the balance sheet.
Hope that helps