What is the U.S. rap rank for the song with a U.S. R&B 23 rank?
CREATE TABLE "singles" (
  "year" real,
  "u_s" text,
  "u_s_r_b" text,
  "u_s_rap" text,
  "album" text
);
SELECT "u_s_rap" FROM "singles" WHERE "u_s_r_b"='23';