Given the task definition and input, reply with output. In this task, you're given a passage, further information available on a particular linked term from the statement, and an answer term. Your job is to generate a question that can use the information provided to obtain the given answer. You should use the information on both passage and link information to create the question. Note that the answer to the question should be exactly the given answer, and if the answer is none, the answer to the question shouldn't be obtainable from the passage or linked information.

Passage: The Settlers: Rise of an Empire () is a city-building game with real-time strategy elements, developed by Blue Byte and published by Ubisoft. Released for Microsoft Windows in September 2007, it is the seventh game in The Settlers series. In March 2008, Blue Byte released an expansion, The Settlers: Rise of an Empire - The Eastern Realm (), featuring new single-player campaign missions, new maps for both single-player and multiplayer modes, and an enhanced map editor. In September, they released The Settlers: Rise of an Empire - Gold Edition, containing the original game plus the Eastern Realm expansion, and additional single and multiplayer maps. The Gold Edition was also released on Steam and Uplay. In 2015, it was released on GOG.com, and in 2018, it was re-released as The Settlers: Rise of an Empire - History Edition.
Link Information: Ubi Soft (formally named Ubi Soft Entertainment S.A.) was founded by the brothers on 28 March 1986. Answer: 21
How long had Ubisoft been in business when they published The Settlers: Rise of an Empire?