Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_name_3 (cars_per_set INTEGER, operator VARCHAR)
### Question:
Tell me the sum of cars per set for operator of london midland
### Answer:
SELECT SUM(cars_per_set) FROM table_name_3 WHERE operator = "london midland"