what is the capacity when the home city is zagreb and the manager is zlatko kranjčar?
CREATE TABLE "summaries" (
  "team" text,
  "manager" text,
  "home_city" text,
  "stadium" text,
  "capacity" real
);
SELECT AVG("capacity") FROM "summaries" WHERE "home_city"='zagreb' AND "manager"='zlatko kranjčar';