When 1873-12-25 is the founding date how many organizations are there?
CREATE TABLE "national_panhellenic_conference_npc" (
  "letters" text,
  "organization" text,
  "nickname" text,
  "founding_date" text,
  "founding_university" text,
  "type" text,
  "canadian_chapters" text
);
SELECT COUNT("organization") FROM "national_panhellenic_conference_npc" WHERE "founding_date"='1873-12-25';