Table schema:
CREATE TABLE table_name_4 (prr_class VARCHAR, build_date VARCHAR, wheel_arrangement VARCHAR, service VARCHAR)

Question: What is the PRR class of the freight train built in 1967 with a b-b wheel arrangement?
SQL: SELECT prr_class FROM table_name_4 WHERE wheel_arrangement = "b-b" AND service = "freight" AND build_date = "1967"