Definition: In this task, you're given a question, along with a context passage. The passage will not have a direct answer to the question, but can include some information and a clue for the answer. Assuming you can only obtain information about one entity in the passage, your job is to determine whether information from the passage can be used to answer the question. Indicate your choice as `a` for Yes or `b` for No.
Input: Question: How many years after Ivan IV of Russia came to power did he conquer the Dorpat area? Passage:With the Treaty of Pozvol, concluded in 1557, the Livonian Confederation had turned to Poland-Lithuania for protection, triggering Ivan IV of Russia's intervention in what was to become the Livonian War. In 1558, Ivan IV had conquered the Dorpat (Tartu) area, annihilating the Bishopric of Dorpat. With the Treaty of Vilnius of 31 August 1559, Gotthard von Kettler, Grand Master of the Livonian Order, had put the order's lands under protection of Polish king and Grand Duke of Lithuania, Sigismund II Augustus. The order ceded about one seventh of its territory, allowed Sigismund to garrison its most important castles, and agreed to share with him any conquests made from Ivan IV. The alliance was intended to neutralize the imminent threat of annexation of the order's lands by Russia, yet despite earning military support from Polish-Lithuanian chancellor Mikołaj "the Black" Radziwiłł, Kettler was defeated in Ergeme (Ermes, 1560) and unable to prevent the occupation of most of Livonia by Russian forces. After the treaty, the disintegrating order agreed to secularization if necessary, and since Sigismund was reluctant to support it militarily, continued its search for a protector at the courts of Denmark-Norway and the Holy Roman Emperor.


b