What is the hardness for the alloy that is liquid at 243 degrees C?
CREATE TABLE "alloys_for_mechanical_composition" (
  "usage" text,
  "sn_sb_pct" text,
  "liquid_at_c" text,
  "casting_at_c" text,
  "remelting_at_c" text,
  "hardness" text
);
SELECT "hardness" FROM "alloys_for_mechanical_composition" WHERE "liquid_at_c"='243';