How many episodes of 30 minutes were written by John Sullivan?
CREATE TABLE table_17641206_4 (
    duration VARCHAR,
    written_by VARCHAR
)
SELECT COUNT(duration) FROM table_17641206_4 WHERE written_by = "John Sullivan"
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: How many episodes of 30 minutes were written by John Sullivan? ### Input: CREATE TABLE table_17641206_4 (
    duration VARCHAR,
    written_by VARCHAR
) ### Response: SELECT COUNT(duration) FROM table_17641206_4 WHERE written_by = "John Sullivan"