user: Question: What is the total number of acres at sai tso wan, opening before 1978?
Columns: ['Landfill', 'Location', 'Acres', 'Opened', 'Capacity', 'Status', 'Rehab Period']
Types: ['text', 'text', 'real', 'real', 'text', 'text', 'text']
Sample row: ['Gin Drinkers Bay', 'Kwai Tsing District', 29.0, 1960.0, '3.5 million tonnes', 'Closed', '1999–2000']
SQL:

assistant: SELECT SUM("Acres") FROM "Table" WHERE "Landfill" = 'sai tso wan' AND "Opened" < 1978.0;