Who wrote the episodes with 7.70 u.s. viewers (million) ?
CREATE TABLE "table1_27117365_1" (
  "no_in_series" real,
  "no_in_season" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" text,
  "u_s_viewers_million" text
);
SELECT "written_by" FROM "table1_27117365_1" WHERE "u_s_viewers_million"='7.70';