What is 4zr's callsign?
CREATE TABLE table_8764 (
    "Callsign" text,
    "Frequency" text,
    "Band" text,
    "On-air ID" text,
    "Purpose" text
)
SELECT "Callsign" FROM table_8764 WHERE "On-air ID" = '4zr'
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 4zr's callsign? ### Input: CREATE TABLE table_8764 (
    "Callsign" text,
    "Frequency" text,
    "Band" text,
    "On-air ID" text,
    "Purpose" text
) ### Response: SELECT "Callsign" FROM table_8764 WHERE "On-air ID" = '4zr'