Below is an instruction that describes a task. Write a response that appropriately completes the request.

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

### Inputs:
table_name: table, columns: ['Class to 1928', 'Class from 1928', 'Seats', 'Quantity', 'Year(s) of Manufacture', 'Remarks']

### Response:
SELECT AVG Quantity FROM table WHERE Year(s) of Manufacture = 1921/23 AND Seats = 40