Table schema:
CREATE TABLE table_name_22 (max_speed__km_h_ INTEGER, quantity_built VARCHAR, year_built VARCHAR)

Question: What is the max speed of the unit with an 8+4 quantity built before 1971?
SQL: SELECT SUM(max_speed__km_h_) FROM table_name_22 WHERE quantity_built = "8+4" AND year_built < 1971