What was the final number for the winning manufacturer with Mercedes-benz, and a circuit of hockenheimring?
CREATE TABLE "race_calendar_and_winners" (
  "round" real,
  "circuit" text,
  "date" text,
  "fastest_lap" text,
  "winning_driver" text,
  "winning_team" text,
  "winning_manufacturer" text
);
SELECT COUNT("round") FROM "race_calendar_and_winners" WHERE "winning_manufacturer"='mercedes-benz' AND "circuit"='hockenheimring';