user: Question: On what surface was the game played with a score of  6–4, 6–4?
Columns: ['Outcome', 'Year', 'Championship', 'Surface', 'Partner', 'Opponents', 'Score']
Types: ['text', 'real', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Runner-up', 1969.0, 'US Open', 'Grass', 'Margaret Court', 'Françoise Dürr Darlene Hard', '0–6, 6–4, 6–4']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Score" = '6–4, 6–4';