Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_1776943_1 ( broadcast_date VARCHAR, viewers__in_millions_ VARCHAR, archive VARCHAR )

### Question ###
Name the broadcast date for 6.4 million viewers for the archive of 16mm t/r

### Accurate SQL ###

SELECT broadcast_date FROM table_1776943_1 WHERE viewers__in_millions_ = "6.4" AND archive = "16mm t/r"