When did series 6 start?
CREATE TABLE table_2978 (
    "Series" real,
    "Start date" text,
    "End date" text,
    "Episodes" real,
    "Average viewers (millions)" text
)
SELECT "Start date" FROM table_2978 WHERE "Series" = '6'
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: When did series 6 start? ### Input: CREATE TABLE table_2978 (
    "Series" real,
    "Start date" text,
    "End date" text,
    "Episodes" real,
    "Average viewers (millions)" text
) ### Response: SELECT "Start date" FROM table_2978 WHERE "Series" = '6'