I'm not sure what this question means.

"One month’s advertising was expended in accordance with the agreement made
with the newspaper on December 1."

It corresponds with the following question.

"Contracted with the local newspaper for three months of advertising and
paid in full the total fee of $600."

December 1:
Debit Prepaid advertising $600
Credit Cash $600

December 31
Debit Advertising Expense 200
Credit prepaid advertising 200