CREATE TABLE table_7218 ("Date" TEXT, "Tournament" TEXT, "Winning score" TEXT, "Margin of victory" TEXT, "Runner ( s ) -up" TEXT)

Which tournament had a margin of victory of 6 strokes?
SELECT "Tournament" FROM table_7218 WHERE "Margin of victory" = '6 strokes'
SELECT "Tournament" FROM "table_7218" WHERE "Margin of victory" = '6 strokes'