can someone explain to me the right answer ? thanks

Newstime magazine, a monthly publication, sold 300 annual subscriptions for $50 each during 2020 . Half of the subscriptions were sold at the beginning of the year, and the rest were sold July 1. Assuming that no adjustments were previously made, the amount of the adjusting entry to recognize revenue on December 31,2020 is $7,500 $15,000 $11,250 \$33,750