CREATE TABLE table_11998 ("Date" CLOB, "Round" CLOB, "Attendance" CLOB, "Opposition" CLOB, "Stadium" CLOB)

What round was adelaide united the opposition with an attendance of 18,345?
SELECT "Round" FROM table_11998 WHERE "Opposition" = 'adelaide united' AND "Attendance" = '18,345'
SELECT "Round" FROM "table_11998" WHERE "Attendance" = '18,345' AND "Opposition" = 'adelaide united'