What is the location attendance of the game with A. Horford (10) as the highest rebounds and J. Johnson (21) as the highest points?
CREATE TABLE "playoffs" (
  "game" real,
  "date" text,
  "team" text,
  "score" text,
  "high_points" text,
  "high_rebounds" text,
  "high_assists" text,
  "location_attendance" text,
  "series" text
);
SELECT "location_attendance" FROM "playoffs" WHERE "high_rebounds"='a. horford (10)' AND "high_points"='j. johnson (21)';