CREATE TABLE table_49921 ("Tie no" TEXT, "Home team" TEXT, "Score" TEXT, "Away team" TEXT, "Date" TEXT)

What is Tie No., when Away Team is 'Manchester United'?
SELECT "Tie no" FROM table_49921 WHERE "Away team" = 'manchester united'
SELECT "Tie no" FROM "table_49921" WHERE "Away team" = 'manchester united'