What is the average quantity for coaches manufactured in 1921/23, and had 40 seats?
CREATE TABLE table_name_87 (
    quantity INTEGER,
    year_s__of_manufacture VARCHAR,
    seats VARCHAR
)
SELECT AVG(quantity) FROM table_name_87 WHERE year_s__of_manufacture = "1921/23" AND seats = "40"
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 quantity for coaches manufactured in 1921/23, and had 40 seats? ### Input: CREATE TABLE table_name_87 (
    quantity INTEGER,
    year_s__of_manufacture VARCHAR,
    seats VARCHAR
) ### Response: SELECT AVG(quantity) FROM table_name_87 WHERE year_s__of_manufacture = "1921/23" AND seats = "40"