What is the largest ration with an ordinary value of 84 zolotnik?
CREATE TABLE "apothecaries_system" (
  "unit" text,
  "russian" text,
  "translation" text,
  "ratio" real,
  "metric_value" text,
  "avoirdupois_value" text,
  "ordinary_value" text
);
SELECT MAX("ratio") FROM "apothecaries_system" WHERE "ordinary_value"='84 zolotnik';