how many years apart were the two garratts on the southern fuegian railway produced ?
CREATE TABLE table_204_637 (
    id number,
    "type" text,
    "gauge" text,
    "railway" text,
    "works no." text,
    "year" text,
    "builder" text
)
SELECT MAX("year") - MIN("year") FROM table_204_637 WHERE "railway" = 'southern fuegian railway'
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: how many years apart were the two garratts on the southern fuegian railway produced ? ### Input: CREATE TABLE table_204_637 (
    id number,
    "type" text,
    "gauge" text,
    "railway" text,
    "works no." text,
    "year" text,
    "builder" text
) ### Response: SELECT MAX("year") - MIN("year") FROM table_204_637 WHERE "railway" = 'southern fuegian railway'