user: Question: What is the highest play-offs that have stevenage borough as the club, and a total greater than 21?
Columns: ['Player', 'Club', 'League', 'Play-offs', 'FA Cup', 'FA Trophy', 'Total']
Types: ['text', 'text', 'real', 'real', 'real', 'real', 'real']
Sample row: ['Giuliano Grazioli', 'Barnet', 29.0, 0.0, 0.0, 0.0, 29.0]
SQL:

assistant: SELECT MAX("Play-offs") FROM "Table" WHERE "Club" = 'stevenage borough' AND "Total" > 21.0;