Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: 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

### Accurate SQL ###

SELECT SUM(cars_per_set) FROM table_name_3 WHERE operator = "london midland"