Suspense accounts- how can this be a debit balance?

Hi all,
I am looking at practice questions, the question says:

When a trial balance was prepared, two ledger accounts were omitted:
Discounts received £6,150
Discounts allowed £7,500

What was the balance on the suspense account?
(It then gives 4 possible answers:

Debit £1,350
Credit £1,350
Debit £13,650
Credit £13,650

I thought the answer was credit £1,350, as the debit side (discounts allowed) is £1,350 more than the credit side (discounts received). Therefore, surely the credit side needs £1,350 to balance the two.
However, the book shows £1,350 debit to be the answer- can someone explain why this is please, as I don't understand?

Thanks.