Commissioner's answer.

(a) The Commissioner may, within such time as may be directed by the Secretary, furnish a written statement to the Secretary in answer to the appellant's petition, including such explanation of the reasons for the action as may be necessary and supplying a copy to the appellant. (b) Within 20 days from the date of such answer, the appellant may file a reply statement directed only to such new points of argument as may be raised in the Commissioner's answer.