You will be given a definition of a task first, then an example. Follow the example to solve a new instance of the task.
In this task you will be given an answer to a question. You need to generate a question. The answer given should be a correct answer for the generated question.

This list contains the top 25 accounts with the most followers on the social photo-sharing platform Instagram. As of May 2018, the most followed user is Instagram's own account, with over 235 million followers. Selena Gomez is the most followed individual, with over 137 million followers. Ten accounts have exceeded 100 million followers on the site.
Solution: who has the maximum number of followers on instagram
Why? The answer is talking about the Instagram accounts that have the most followers. The question asking about the maximum number of followers. So this is a good example.

New input: The Second Battle of the Marne (French: Seconde Bataille de la Marne), or Battle of Reims (15 July -- 6 August 1918) was the last major German offensive on the Western Front during the First World War. The attack failed when an Allied counterattack, supported by several hundred tanks, overwhelmed the Germans on their right flank, inflicting severe casualties. The German defeat marked the start of the relentless Allied advance which culminated in the Armistice with Germany about 100 days later.
Solution:
how long did the second battle of marne last