Answer:
May 9th
Explanation:
When a company uses a cash basis accounting, it records its revenues and expenses on the day that the money is received or paid respectively. In this case, the supplies were purchased on May 1st, delivered on May 5th, used on May 8th, but paid on May 9th. And the date of the payment is what matters here.
The journal entry should be as following:
May 9, office supplies.
Dr Supplies expense 3,000
Cr Cash 3,000