เมื่อสหรัฐอเมริกามีคะแนนรวม 274 ปีเฉลี่ยคือเท่าใด
When the United States had a total score of 274 what was the average year?
df = pd.DataFrame(columns=['year', 'total_score', 'country'])
df.loc[(df['total_score'] == "274") & (df['country'] == "united states"), 'year'].mean()