What is the average Round, when Pick # is greater than 70, and when Position is Tackle?
CREATE TABLE "nfl_draft" (
  "round" real,
  "pick_num" real,
  "player" text,
  "position" text,
  "college" text
);
SELECT AVG("round") FROM "nfl_draft" WHERE "pick_num">70 AND "position"='tackle';