What is the mintage (bu) with the artist Royal Canadian Mint Staff and has an issue price (proof) of $54.95?
CREATE TABLE "commemorative_silver_dollar_series" (
  "year" real,
  "theme" text,
  "artist" text,
  "mintage_proof" text,
  "issue_price_proof" text,
  "mintage_bu_clarification_needed" text,
  "issue_price_bu_clarification_needed" text
);
SELECT "mintage_bu_clarification_needed" FROM "commemorative_silver_dollar_series" WHERE "artist"='Royal Canadian Mint Staff' AND "issue_price_proof"='$54.95';