Table: railway_vehicles_2
Columns: year
quantity
manufacturer
serial_number
tvr_numbers
gwr_numbers

Question: What is the average Year that has a Quantity of 10, and a GWR Numbers of 409, 290, 315, 317–321, 324, 333?
SQL: SELECT AVG("year") FROM railway_vehicles_2 WHERE "quantity" = 10 AND "gwr_numbers" = '409, 290, 315, 317–321, 324, 333'