user: ### NOW ANSWER:
Question: Which Quantity has a Designation of Type 4?
Columns: ['Designation', 'Car numbers', 'Manufacturer', 'Model No.', 'First used', 'Quantity']
Types: ['text', 'text', 'text', 'text', 'text', 'real']
Sample row: ['Type 1', '101–126', 'Bombardier', 'none', '1986', 26.0]
SQL:

assistant: SELECT AVG("Quantity") FROM "Table" WHERE "Designation" = 'Type 4';