What is the rank 6 lowest win who's first win was at the 1950 British Grand Prix?
CREATE TABLE "world_championship_grand_prix_wins_by_en" (
  "rank" real,
  "engine" text,
  "wins" real,
  "first_win" text,
  "latest_win" text
);
SELECT MIN("wins") FROM "world_championship_grand_prix_wins_by_en" WHERE "rank">6 AND "first_win"='1950 british grand prix';