Which Quantity has an Axle arrangement of 2′c h2?
CREATE TABLE "passenger_and_express_train_locomotives" (
  "class" text,
  "railway_number_s" text,
  "drg_number_s" text,
  "quantity" real,
  "year_s_of_manufacture" text,
  "axle_arrangement" text
);
SELECT AVG("quantity") FROM "passenger_and_express_train_locomotives" WHERE "axle_arrangement"='2′c h2';