Tell me the totla number of goal difference for goals against of 30 and played less than 18
CREATE TABLE "final_league_position" (
  "team" text,
  "played" real,
  "draw" real,
  "lost" real,
  "goals_for" real,
  "goals_against" real,
  "goal_difference" real,
  "points" real
);
SELECT COUNT("goal_difference") FROM "final_league_position" WHERE "goals_against"=30 AND "played"<18;