CREATE TABLE table_41788 ("Landfill" TEXT, "Location" TEXT, "Acres" FLOAT, "Opened" FLOAT, "Capacity" TEXT, "Status" TEXT, "Rehab Period" TEXT)

What is the total number of acres at Sai Tso Wan, opening before 1978?
SELECT COUNT("Acres") FROM table_41788 WHERE "Landfill" = 'sai tso wan' AND "Opened" < '1978'
SELECT COUNT("Acres") FROM "table_41788" WHERE "Landfill" = 'sai tso wan' AND "Opened" < '1978'