Tell me the sum of cars per set for operator of london midland
CREATE TABLE table_32100 (
    "Class" text,
    "Operator" text,
    "No. Built" real,
    "Year Built" text,
    "Cars per Set" real
)
SELECT SUM("Cars per Set") FROM table_32100 WHERE "Operator" = 'london midland'
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: Tell me the sum of cars per set for operator of london midland ### Input: CREATE TABLE table_32100 (
    "Class" text,
    "Operator" text,
    "No. Built" real,
    "Year Built" text,
    "Cars per Set" real
) ### Response: SELECT SUM("Cars per Set") FROM table_32100 WHERE "Operator" = 'london midland'