instruction:
In this task, you're given a context, 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 context 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 context or linked information.
question:
Context: He fought in Operation Barbarossa, the German invasion of the Soviet Union, and claimed his first aerial victory on 8 August 1941. Link Information: none Answer: none
answer:
How many days did Operation Barbarossa last?


question:
Context: When he was seventy, Eli decided to move back to San Francisco. By 1888 Eli was in San Francisco with his daughter, Link Information: none Answer: none
answer:
Was San Francisco the capital of California in 1888?


question:
Context: The results included the failed First Anglo-Afghan War of 1838, the First Anglo-Sikh War of 1845, the Second Anglo-Sikh War of 1848, the Second Anglo-Afghan War of 1878 Link Information:  fought between the British East India Company and the Emirate of Afghanistan from 1839 to 1842. Answer: First Anglo-Afghan War
answer:

Of the wars fought in the 1840s, how long did the longest one last?