(a) Within 20 days of receipt of the notice of violation and hearing, but no later than five days before the date of the hearing, whichever is shorter, the respondent shall serve upon the commissioner an answer, signed by the respondent or his attorney.

(b) The respondent shall specify in the answer which allegations are admitted, which allegations are denied and which allegations the respondent lacks sufficient information upon which to form an opinion as to the allegation.

(c) The respondent's answer may contain affirmative defenses, in which event the answer shall contain a statement of any facts which constitute the grounds of the affirmative defense.

(d) The failure to file an answer or the failure by the respondent to appear on the return date or at the hearing shall constitute a default and a waiver of hearing upon proof of service of a notice of violation and hearing.