user: Question: Name the broadcast date for 6.4 million viewers for the archive of 16mm t/r
Columns: ['Episode', 'Broadcast date', 'Run time', 'Viewers (in millions)', 'Archive']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['" A Land of Fear "', '8August1964', '24:24', '6.9', '16mm t/r']
SQL:

assistant: SELECT "Broadcast date" FROM "Table" WHERE "Viewers (in millions)" = '6.4' AND "Archive" = '16mm t/r';