What is the average length in feet of the bridges?
CREATE TABLE bridge (
    architect_id number,
    id number,
    name text,
    location text,
    length_meters number,
    length_feet number
)

CREATE TABLE mill (
    architect_id number,
    id number,
    location text,
    name text,
    type text,
    built_year number,
    notes text
)

CREATE TABLE architect (
    id text,
    name text,
    nationality text,
    gender text
)
SELECT AVG(length_feet) FROM bridge
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 average length in feet of the bridges? ### Input: CREATE TABLE bridge (
    architect_id number,
    id number,
    name text,
    location text,
    length_meters number,
    length_feet number
)

CREATE TABLE mill (
    architect_id number,
    id number,
    location text,
    name text,
    type text,
    built_year number,
    notes text
)

CREATE TABLE architect (
    id text,
    name text,
    nationality text,
    gender text
) ### Response: SELECT AVG(length_feet) FROM bridge