What is the weight with the shape of scalloped, and that is a size of 20mm (across scallops)?
CREATE TABLE "aluminium_series" (
  "denomination" text,
  "metal" text,
  "weight" text,
  "shape" text,
  "size" text
);
SELECT "weight" FROM "aluminium_series" WHERE "shape"='scalloped' AND "size"='20mm (across scallops)';