What manufacturer has a wheel arrangement of 4-6-6-4, and a Class of z-7?
CREATE TABLE "mallet_and_simple_articulated_locomotive" (
  "class" text,
  "wheel_arrangement" text,
  "fleet_number_s" text,
  "manufacturer" text,
  "serial_numbers" text,
  "year_made" text,
  "quantity_made" text,
  "quantity_preserved" text
);
SELECT "manufacturer" FROM "mallet_and_simple_articulated_locomotive" WHERE "wheel_arrangement"='4-6-6-4' AND "class"='z-7';