Name the number of years for 18.5
CREATE TABLE "nascar_sprint_cup_series" (
  "year" real,
  "starts" real,
  "wins" real,
  "top_5" real,
  "top_10" real,
  "poles" real,
  "avg_start" text,
  "avg_finish" text,
  "winnings" text,
  "position" text,
  "team_s" text
);
SELECT COUNT("year") FROM "nascar_sprint_cup_series" WHERE "avg_finish"='18.5';