Final answer:
When adjusting the supplies account for supplies used, a debit entry is made to the Supplies Expense account and a credit entry to the Supplies account for the amount used.
Step-by-step explanation:
When adjusting the supplies account, you need to account for the supplies used during the month. Since supplies worth $350 were used, you would make a debit entry to the Supplies Expense account and a credit entry to the Supplies account for $350.
Therefore, the correct adjustment would be option 3) A debit to the supplies expense account and a credit to the supplies account for 350.