What is the PRR class of the freight train built in 1967 with a b-b wheel arrangement?
CREATE TABLE "emd" (
  "prr_class" text,
  "builder_s_model" text,
  "build_date" text,
  "total_produced" real,
  "wheel_arrangement" text,
  "service" text,
  "power_output" text
);
SELECT "prr_class" FROM "emd" WHERE "wheel_arrangement"='b-b' AND "service"='freight' AND "build_date"='1967';