what was Casey Martin's minimum yearly earnings?
CREATE TABLE table_21173 (
    "Year" real,
    "Tournaments played" real,
    "Cuts made" real,
    "Wins" real,
    "Best finish" text,
    "Earnings ( $ )" real,
    "Money list rank" text
)
SELECT MIN("Earnings ( $ )") FROM table_21173
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 was Casey Martin's minimum yearly earnings? ### Input: CREATE TABLE table_21173 (
    "Year" real,
    "Tournaments played" real,
    "Cuts made" real,
    "Wins" real,
    "Best finish" text,
    "Earnings ( $ )" real,
    "Money list rank" text
) ### Response: SELECT MIN("Earnings ( $ )") FROM table_21173