What is the sum of all win% with average home/total attendance of 3,927 (19,633)?
CREATE TABLE "year_by_year_performance" (
  "coach" text,
  "season" text,
  "record" text,
  "home" text,
  "away" text,
  "win_pct" real,
  "average_total_home_attendance" text
);
SELECT SUM("win_pct") FROM "year_by_year_performance" WHERE "average_total_home_attendance"='3,927 (19,633)';