In any case covered by § 4.816 or § 4.817, the applicant or recipient shall file an answer. Said answer shall admit or deny each allegation of the notice, unless the applicant or recipient is without knowledge, in which case the answer shall so state, and the statement will be considered a denial. Failure to file an answer shall be deemed an admission of all allegations of fact in the notice. Allegations of fact in the notice not denied or controverted by answer shall be deemed admitted. Matters alleged in the answer as affirmative defenses shall be separately stated and numbered. The answer under § 4.816 shall be filed within 20 days from the date of service of the notice of hearing. The answer under § 4.817 shall be filed within 20 days of service of the notice of opportunity to request a hearing.