Tell me the sum of round for record of 6-3
CREATE TABLE "mixed_martial_arts_record" (
  "res" text,
  "record" text,
  "opponent" text,
  "method" text,
  "round" real,
  "time" text,
  "location" text
);
SELECT SUM("round") FROM "mixed_martial_arts_record" WHERE "record"='6-3';