Which is the lowest 1980 growth that had 2,610 in 1970?
CREATE TABLE table_53640 (
    "City" text,
    "1970" real,
    "1980" real,
    "1990" real,
    "2000" real,
    "2010 est." real
)
SELECT MIN("1980") FROM table_53640 WHERE "1970" = '2,610'
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: Which is the lowest 1980 growth that had 2,610 in 1970? ### Input: CREATE TABLE table_53640 (
    "City" text,
    "1970" real,
    "1980" real,
    "1990" real,
    "2000" real,
    "2010 est." real
) ### Response: SELECT MIN("1980") FROM table_53640 WHERE "1970" = '2,610'