user: Question: What is the average net yds for the player who had a long of 68 and started after 1984?
Columns: ['Rank', 'Name', 'Attempts', 'Net Yds', 'Yds/Att', 'Touchdowns', 'Long', 'Start']
Types: ['real', 'text', 'real', 'real', 'real', 'real', 'real', 'real']
Sample row: [1.0, 'Mike Hart', 1015.0, 5040.0, 5.0, 41.0, 64.0, 2004.0]
SQL:

assistant: SELECT AVG("Net Yds") FROM "Table" WHERE "Long" = 68.0 AND "Start" > 1984.0;