user: Question: How many people attended the match when Manchester United played against the Hearts?
Columns: ['Date', 'Opponents', 'H / A', 'Result F – A', 'Attendance']
Types: ['text', 'text', 'text', 'text', 'real']
Sample row: ['30 July 1989', 'Thailand National XI', 'A', '1 – 1 (4 – 2 p )', 12000.0]
SQL:

assistant: SELECT SUM("Attendance") FROM "Table" WHERE "Opponents" = 'Hearts';