how many acc football titles have been won by the institution nicknamed tar heels?
CREATE TABLE "member_schools" (
  "institution" text,
  "nickname" text,
  "location" text,
  "founded" real,
  "joined_acc" real,
  "school_type" text,
  "acc_football_titles" real
);
SELECT "acc_football_titles" FROM "member_schools" WHERE "nickname"='Tar Heels';