What's the highest annual interchange for wimbledon railway station?
CREATE TABLE "references" (
  "rank" real,
  "railway_station" text,
  "annual_entry_exit_millions_2011_12" real,
  "annual_interchanges_millions_2011_12" real,
  "total_passengers_millions_2011_12" real,
  "location" text,
  "number_of_platforms" real
);
SELECT MAX("annual_interchanges_millions_2011_12") FROM "references" WHERE "railway_station"='wimbledon';