Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_20967430_4 (prod_code VARCHAR, written_by VARCHAR)
### Question:
What is the production code of the episode written by Jack Carrerrow?
### Answer:
SELECT prod_code FROM table_20967430_4 WHERE written_by = "Jack Carrerrow"