user: Question: What is the total year of the winner who plays the halfback position with a % of points possible of 80.64%?
Columns: ['Year', 'Winner', 'School', 'Position', 'Points', '% of Points Possible']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1935.0, 'Jay Berwanger Category:Articles with hCards *', 'Chicago', 'Halfback', '84', '43.08%']
SQL:

assistant: SELECT SUM("Year") FROM "Table" WHERE "Position" = 'halfback' AND "% of Points Possible" = '80.64%';