Name the round for engine of ford cosworth dfv 3.0 v8 with chassis fo 751
CREATE TABLE "drivers_and_constructors" (
  "entrant" text,
  "constructor" text,
  "chassis" text,
  "engine" text,
  "tyre" text,
  "driver" text,
  "rounds" text
);
SELECT "rounds" FROM "drivers_and_constructors" WHERE "engine"='ford cosworth dfv 3.0 v8' AND "chassis"='751';