user: Question: Name the sum of year for Penrith Panthers opponent
Columns: ['Margin', 'Score', 'Opponent', 'Venue', 'Year']
Types: ['real', 'text', 'text', 'text', 'real']
Sample row: [66.0, '66–0', 'South Sydney Rabbitohs', 'Sydney Football Stadium', 2006.0]
SQL:

assistant: SELECT SUM("Year") FROM "Table" WHERE "Opponent" = 'Penrith Panthers';