Enrollment that has a School of south central (union mills) has what sum?
CREATE TABLE "indiana_high_school_athletics_conference" (
  "school" text,
  "city" text,
  "mascot" text,
  "enrollment" real,
  "county" text
);
SELECT SUM("enrollment") FROM "indiana_high_school_athletics_conference" WHERE "school"='south central (union mills)';