39 CFR 956.8: (Rule 8) Answer to petition.

Within 15 days from the date of receiving the Notice of Docketing, the Postal Service's representative must file an answer to the petition and attach all available relevant records and documents in support of the Postal Service's debt claim. The answer must provide a clear and thorough description of the basis for the Postal Service's determination of the alleged debt and its calculation of the alleged debt amount.