A group of adults and children spent a total of $420 for tickets and food at the circus. Tickets to the circus cost $20 per adult and $10 per child. If the group spent an average of $21 per person for tickets and food, and there were the same number of adults as children in the group, what was the total amount that the group spent on food at the circus?

组合成人和儿童共计花费420美元购买马戏团的门票和食物，成人每人20美元，儿童每人10美元。如果成人和儿童的人数相同，同一组人平均花费21美元，那么该组人在马戏团购买食物的共计花费是多少？答案是：该组人在马戏团购买食物的共计花费是210美元。