Which engine of Rob Walker Racing Team has 47 points and F tyres?
CREATE TABLE "complete_formula_one_world_championship_" (
  "year" real,
  "entrant" text,
  "chassis" text,
  "engine" text,
  "tyres" text,
  "points" text
);
SELECT "engine" FROM "complete_formula_one_world_championship_" WHERE "points"='47' AND "tyres"='f' AND "entrant"='rob walker racing team';