what is the sum of laps when grid is less than 20 and johnny herbert is driving?
CREATE TABLE table_56492 (
    "Driver" text,
    "Constructor" text,
    "Laps" real,
    "Time/Retired" text,
    "Grid" real
)
SELECT SUM("Laps") FROM table_56492 WHERE "Grid" < '20' AND "Driver" = 'johnny herbert'
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: what is the sum of laps when grid is less than 20 and johnny herbert is driving? ### Input: CREATE TABLE table_56492 (
    "Driver" text,
    "Constructor" text,
    "Laps" real,
    "Time/Retired" text,
    "Grid" real
) ### Response: SELECT SUM("Laps") FROM table_56492 WHERE "Grid" < '20' AND "Driver" = 'johnny herbert'