How many have been replaced where the appointment date is 10 December 2007 and the manner of departure is quit?
CREATE TABLE "managerial_changes" (
  "team" text,
  "outgoing_manager" text,
  "manner_of_departure" text,
  "date_of_vacancy" text,
  "replaced_by" text,
  "date_of_appointment" text
);
SELECT COUNT("replaced_by") FROM "managerial_changes" WHERE "date_of_appointment"='10 December 2007' AND "manner_of_departure"='Quit';