Table schema:
CREATE TABLE table_name_50 (engine_capacity VARCHAR, model VARCHAR, mpg_us_extra_urban VARCHAR, transmission VARCHAR, mpg_us_urban VARCHAR)

Question: What is the total engine capacity of the a4 transmission, which has an urban mpg-US greater than 19, an mpg-us extra-urban greater than 38.6, and an aveo model?
SQL: SELECT COUNT(engine_capacity) FROM table_name_50 WHERE transmission = "a4" AND mpg_us_urban > 19 AND mpg_us_extra_urban > 38.6 AND model = "aveo"