What is the production code for the episode that had 9.18 million viewers (U.S.)?
CREATE TABLE table_73321 (
    "No." real,
    "#" real,
    "Title" text,
    "Directed by" text,
    "Written by" text,
    "U.S. viewers (million)" text,
    "Original air date" text,
    "Production code" real
)
SELECT MAX("Production code") FROM table_73321 WHERE "U.S. viewers (million)" = '9.18'
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: What is the production code for the episode that had 9.18 million viewers (U.S.)? ### Input: CREATE TABLE table_73321 (
    "No." real,
    "#" real,
    "Title" text,
    "Directed by" text,
    "Written by" text,
    "U.S. viewers (million)" text,
    "Original air date" text,
    "Production code" real
) ### Response: SELECT MAX("Production code") FROM table_73321 WHERE "U.S. viewers (million)" = '9.18'