What is the sum of enrollments for schools located in Culver?
CREATE TABLE "membership" (
  "school_ihsaa_i_dnum" text,
  "location" text,
  "mascot" text,
  "enrollment" real,
  "ihsaa_class" text,
  "num_county" text,
  "year_joined" real
);
SELECT SUM("enrollment") FROM "membership" WHERE "location"='culver';