What year was the brabham bt46 bt48 bt49 Chassis common?
CREATE TABLE table_15707 (
    "Year" real,
    "Entrant" text,
    "Chassis" text,
    "Engine" text,
    "Tyres" text,
    "Points" real
)
SELECT AVG("Year") FROM table_15707 WHERE "Chassis" = 'brabham bt46 bt48 bt49'
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 year was the brabham bt46 bt48 bt49 Chassis common? ### Input: CREATE TABLE table_15707 (
    "Year" real,
    "Entrant" text,
    "Chassis" text,
    "Engine" text,
    "Tyres" text,
    "Points" real
) ### Response: SELECT AVG("Year") FROM table_15707 WHERE "Chassis" = 'brabham bt46 bt48 bt49'