user: Question: How many millions of U.S viewers are there when the director is Andy Wolk?
Columns: ['Series #', 'Title', 'Directed by', 'Written by', 'Original air date', 'Production code', 'U.S. viewers (million)']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, '"Pilot"', 'Bronwen Hughes', 'Michael Sardo', 'January20,2011', 'FL101-75', '3.88']
SQL:

assistant: SELECT SUM("U.S. viewers (million)") FROM "Table" WHERE "Directed by" = 'Andy Wolk';