What is the average finish that has 24 as the start, with a year after 1987?
CREATE TABLE "indianapolis_500" (
  "year" real,
  "chassis" text,
  "engine" text,
  "start" real,
  "finish" real,
  "entrant" text
);
SELECT AVG("finish") FROM "indianapolis_500" WHERE "start"=24 AND "year">1987;