Table: episodes_39
Columns: col
col_2
title
directed_by
written_by
original_air_date
production_code
u_s_viewers_millions

Question: What was the number of episodes whose production code is 7ABB21?
SQL: SELECT COUNT("col_2") FROM episodes_39 WHERE "production_code" = '7ABB21'

Question: Who wrote episode number 18?
SQL: SELECT "written_by" FROM episodes_39 WHERE "col_2" = 18