What is the total number of acres at Sai Tso Wan, opening before 1978?
CREATE TABLE table_41788 (
    "Landfill" text,
    "Location" text,
    "Acres" real,
    "Opened" real,
    "Capacity" text,
    "Status" text,
    "Rehab Period" text
)
SELECT COUNT("Acres") FROM table_41788 WHERE "Landfill" = 'sai tso wan' AND "Opened" < '1978'
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: What is the total number of acres at Sai Tso Wan, opening before 1978? ### Input: CREATE TABLE table_41788 (
    "Landfill" text,
    "Location" text,
    "Acres" real,
    "Opened" real,
    "Capacity" text,
    "Status" text,
    "Rehab Period" text
) ### Response: SELECT COUNT("Acres") FROM table_41788 WHERE "Landfill" = 'sai tso wan' AND "Opened" < '1978'