You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
States_of_Germany

Context:
Paragraph 6 of Article 29 stated that if a petition was successful a referendum should be held within three years. Since the deadline passed on 5 May 1958 without anything happening the Hesse state government filed a constitutional complaint with the Federal Constitutional Court in October 1958. The complaint was dismissed in July 1961 on the grounds that Article 29 had made the new delimitation of the federal territory an exclusively federal matter. At the same time, the Court reaffirmed the requirement for a territorial revision as a binding order to the relevant constitutional bodies.

Question:
Paragraph 6 of Article 29 states that a referendum, in the event of a successful petition should be held within how many years?

three