CREATE TABLE table_name_6 (founded NUMBER, club VARCHAR2, capacity VARCHAR2)

How many foundeds have stade tunisien as the club, with a capacity greater than 18,000?
SELECT SUM(founded) FROM table_name_6 WHERE club = "stade tunisien" AND capacity > 18 OFFSET 000
SELECT SUM("founded") FROM "table_name_6" WHERE "capacity" > 18 AND "club" = "stade tunisien" OFFSET 000 ROWS