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_30975 ( "Season no." real, "Series no." real, "Title" text, "Directed by" text, "Written by" text, "Original air date" text, "Production code" real, "U.S. viewers (millions)" text )

### Question ###
What is the last episode in the season that had 3.91 million viewers in the US?

### Accurate SQL ###

SELECT MIN("Season no.") FROM table_30975 WHERE "U.S. viewers (millions)" = '3.91'