How many values for founded when enrollment is 850?
CREATE TABLE "current_member_schools" (
  "school" text,
  "location" text,
  "enrolment" real,
  "founded" real,
  "denomination" text,
  "boys_girls" text,
  "day_boarding" text,
  "school_colors" text
);
SELECT COUNT("founded") FROM "current_member_schools" WHERE "enrolment"=850;