What is the highest quantity of the b ix k.b.sts.b.?
CREATE TABLE "locomotives_and_wagons" (
  "class" text,
  "quantity" real,
  "type" text,
  "delivered" text,
  "k_b_sts_b_class" text,
  "retired" text
);
SELECT MAX("quantity") FROM "locomotives_and_wagons" WHERE "k_b_sts_b_class"='b ix';