user: Question: What's the series number of the episode whose writer is David North?
Columns: ['No. in series', 'No. in season', 'Title', 'Directed by', 'Written by', 'Original air date', 'U.S. viewers (millions)']
Types: ['real', 'real', 'text', 'text', 'text', 'text', 'text']
Sample row: [95.0, 1.0, '"Bury Your Dead"', 'Thomas J. Wright', 'Shane Brennan', 'September25,2007', '13.89']
SQL:

assistant: SELECT "No. in series" FROM "Table" WHERE "Written by" = 'David North';