Among the tweets posted from Santa Fe state in Argentina, how many of them were posted on 31st?
"Sante Fe" is the State; "Argentina" is the Country; posted on 31st refers to Day = 31
SELECT COUNT(T1.TweetID) FROM twitter AS T1 INNER JOIN location AS T2 ON T1.LocationID = T2.LocationID WHERE T1.Day = 31 AND T2.State = 'Santa' AND T2.Country = 'Argentina'