user: Question: When Zachary Sanders is the performer how many first aired are there?
Columns: ['Episode title', 'Subject', 'Music by', 'Lyrics by', 'Performed by', 'First aired']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Conjunction Junction', 'conjunction', 'Bob Dorough', 'Jack Sheldon and Terri Morel', 'Jack Sheldon', '1973']
SQL:

assistant: SELECT COUNT("First aired") FROM "Table" WHERE "Performed by" = 'Zachary Sanders';