What is the production code of the episode directed by David Solomon? 
CREATE TABLE table_21304155_1 (production_code VARCHAR, directed_by VARCHAR)
SELECT production_code FROM table_21304155_1 WHERE directed_by = "David Solomon"
### Context: CREATE TABLE table_21304155_1 (production_code VARCHAR, directed_by VARCHAR) ### Question: What is the production code of the episode directed by David Solomon?  ### Answer: SELECT production_code FROM table_21304155_1 WHERE directed_by = "David Solomon"