Which Grid has Laps of 24, and a Rider of marco melandri?
CREATE TABLE "moto_gp_classification" (
  "rider" text,
  "manufacturer" text,
  "laps" real,
  "time" text,
  "grid" real
);
SELECT SUM("grid") FROM "moto_gp_classification" WHERE "laps"=24 AND "rider"='marco melandri';