Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_64026 ( "Class to 1928" text, "Class from 1928" text, "Seats" text, "Quantity" real, "Year(s) of Manufacture" text, "Remarks" text )

### Question ###
What is the average quantity for coaches manufactured in 1921/23, and had 40 seats?

### Accurate SQL ###

SELECT AVG("Quantity") FROM table_64026 WHERE "Year(s) of Manufacture" = '1921/23' AND "Seats" = '40'