What is the earliest year where the mintage (proof) is 25,000?
CREATE TABLE "commemorative_silver_dollar_series" (
  "year" real,
  "theme" text,
  "artist" text,
  "mintage_proof" text,
  "issue_price_proof" text,
  "mintage_bu_clarification_needed" text,
  "issue_price_bu_clarification_needed" text
);
SELECT MIN("year") FROM "commemorative_silver_dollar_series" WHERE "mintage_proof"='25,000';