Which rider had a speed of 90.57mph?
CREATE TABLE "1970_isle_of_man_lightweight_tt_250cc_fi" (
  "place" real,
  "rider" text,
  "country" text,
  "machine" text,
  "speed" text,
  "time" text,
  "points" real
);
SELECT "rider" FROM "1970_isle_of_man_lightweight_tt_250cc_fi" WHERE "speed"='90.57mph';