what is the total sack for mike green when fumr is less than 0?
CREATE TABLE "defense" (
  "player" text,
  "tackles" real,
  "asst" real,
  "total_tk" real,
  "sack" real,
  "yards" real,
  "fum_r" real
);
SELECT SUM("sack") FROM "defense" WHERE "player"='mike green' AND "fum_r"<0;