user: Question: Which average Opened has a Manufacturer of Vekoma?
Columns: ['Name', 'Style', 'Opened', 'Manufacturer', 'Themed Area']
Types: ['text', 'text', 'real', 'text', 'text']
Sample row: ['The Shock Wave', 'Standing Up Rollercoaster', 1994.0, 'Intamin', 'Action Park']
SQL:

assistant: SELECT AVG("Opened") FROM "Table" WHERE "Manufacturer" = 'Vekoma';