What year did Culver leave?
CREATE TABLE "former_members" (
  "school" text,
  "location" text,
  "mascot" text,
  "num_county" text,
  "year_joined" real,
  "previous_conference" text,
  "year_left" real,
  "new_conference" text
);
SELECT SUM("year_left") FROM "former_members" WHERE "location"='culver';