CREATE TABLE table_51768 ("Home team" TEXT, "Home team score" TEXT, "Away team" TEXT, "Away team score" TEXT, "Venue" TEXT, "Crowd" FLOAT, "Date" TEXT)

Who was Melbourne's away team opponent?
SELECT "Away team" FROM table_51768 WHERE "Home team" = 'melbourne'
SELECT "Away team" FROM "table_51768" WHERE "Home team" = 'melbourne'