Code of Federal Regulations Title 43. Public Lands:  Interior § 43.4.1284 Answer

(a) Any party served with a notice of appeal who wishes to participate in the proceedings on appeal shall file an answer with the Board within 20 days after service of the notice of appeal or statement of reasons where such statement was not included in the notice of appeal.

(b) If additional reasons, written arguments or other documents are filed by the appellant, a party shall have 20 days after service thereof within which to answer. The answer shall state the reasons the party opposes or supports the appeal.