Rule 15 - Amended and Supplemental Pleadings(a) Amendments. A party may amend the petition once as a matter of course at any time before an answer is served. A party may amend an answer at any time within 20 days after it is served. Otherwise a party may amend a pleading only by leave of court or by written consent of all other parties; and leave shall be freely given when justice so requires. A party may file an answer to an amended petition within 10 days after service of the amended petition. (b) Amendments to conform to the evidence. When issues not raised by the petition or an answer are addressed by express or implied consent of the parties, they shall be treated in all respects as if they had been raised in the petition or an answer. Such amendment of the petition or an answer as may be necessary to cause them to conform to the evidence and to raise these issues may be made upon motion of any party at any time, even after judgment; but failure so to amend does not affect the result of any hearing on these issues. If evidence is objected to at a hearing on the ground that it is not within the issues made by the pleadings, the court may allow the pleadings to be amended and shall do so freely when the presentation of the merits of the action will be subserved thereby and the objecting party fails to satisfy the court that the admission of such evidence would prejudice that party. (c) Relation back of amendments. Whenever the position or request asserted in the amended petition or answer arose out of the conduct, transaction, or occurrence set forth or attempted to be set forth in the original petition or answer, the amendment relates back to the date of the original pleading. (d) Supplemental pleadings. Upon motion of a party the court may, upon reasonable notice and upon such terms as are just, permit the party to serve a supplemental pleading setting forth transactions or events which have occurred since the date of the pleading sought to be supplemented.