user: Question: How many have been replaced where the appointment date is 10 December 2007 and the manner of departure is Quit?
Columns: ['Team', 'Outgoing manager', 'Manner of departure', 'Date of vacancy', 'Replaced by', 'Date of appointment']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Sint-Truiden', 'Valère Billen', 'Quit', '18 September 2007', 'Peter Voets (caretaker)', '18 September 2007']
SQL:

assistant: SELECT COUNT("Replaced by") FROM "Table" WHERE "Date of appointment" = '10 December 2007' AND "Manner of departure" = 'Quit';