TASK DEFINITION: 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.
PROBLEM: Context: He commanded the U.S. forces in the Battle of Tirad Pass, 2 December 1899, where General Gregorio del Pilar was killed Link Information: He was promoted to brigadier-general after this event. Answer: 1 

SOLUTION: How long had Gregorio del Pilar been a General for when he was killed?

PROBLEM: Context: In 1972 he became the first Professor of Music at Sussex University Link Information: none Answer: none

SOLUTION: How many students were enrolled at Sussex University the year Mitchell became the first Professor of Music there?

PROBLEM: Context: Horst Hannig claimed his first aerial victory, a Tupolev SB-2, on the first day of Operation Barbarossa, the German invasion of the Soviet Union on 22 June 1941. Link Information: Operation Barbarossa () was the code name for the Axis invasion of the Soviet Union, which started on Sunday, 22 June 1941 Answer: 199

SOLUTION:
How long did the German invasion of Soviet Union that Hannig participated in last?