What is the total of Matches with Goals of 18, and an Average larger than 0.55?
CREATE TABLE "top_goalkeepers" (
  "goalkeeper" text,
  "goals" real,
  "matches" real,
  "average" real,
  "team" text
);
SELECT SUM("matches") FROM "top_goalkeepers" WHERE "goals"=18 AND "average">0.55;