What is the Surface of the match played on October 5, 1987?
CREATE TABLE "doubles_9_3_6" (
  "outcome" text,
  "date" text,
  "tournament" text,
  "surface" text,
  "partner" text,
  "opponents" text,
  "score" text
);
SELECT "surface" FROM "doubles_9_3_6" WHERE "date"='october 5, 1987';