user: Question: How many episodes were written by David J. North & Janet Tamaro?
Columns: ['No. in series', 'No. in season', 'Title', 'Directed by', 'Written by', 'Original air date', 'Production', 'U.S. viewers (in millions)']
Types: ['real', 'real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [11.0, 1.0, '"We Don\'t Need Another Hero"', 'Michael Zinberg', 'Janet Tamaro', 'July11,2011', '2M5601', '6.38']
SQL:

assistant: SELECT COUNT("Original air date") FROM "Table" WHERE "Written by" = 'David J. North & Janet Tamaro';