user: Question: What was the Int'l Debut for a player in the Back position, that also had a Cross Code Debut of RU Australia v Wales?
Columns: ['Player', "Int'l Debut", 'Year', 'Cross Code Debut', 'Date', 'Position']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Dally Messenger', '2nd RU Test Australia v New Zealand', '1907', 'RL New Zealand v Wales', '1 Jan 1908', 'Centre']
SQL:

assistant: SELECT "Int'l Debut" FROM "Table" WHERE "Position" = 'Back' AND "Cross Code Debut" = 'RU Australia v Wales';