instruction:
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.
question:
Passage: Victor (sometimes spelled Viktor) became an officer in the Royal Navy in 1848 and was promoted to Lieutenant in 1854. As a Lieutenant, he served on the first-rate HMS St Jean d'Acre in the Mediterranean under Captain Henry Keppel in 1855; commanded the gunboat HMS Traveller for a few months in 1856 after her launch until she was paid off; served again under Keppel again on the fourth-rate HMS Raleigh in the East Indies and China, until she was wrecked near Macau in 1857. He was recommended for the Victoria Cross for his service in China in 1856. He was promoted to Commander in 1857, and commanded the first-rate sloop HMS Scourge in the Mediterranean. Promoted to Captain in 1859, he took command of the 21-gun corvette HMS Racoon from commissioning in 1863 until 1866, during which time Queen Victoria's second son, Alfred, Duke of Edinburgh (1844–1900) served on board as a lieutenant.
 Link Information: Henry Keppel (14 June 1809 – 17 January 1904 Answer: 46
answer:
How old was Henry Keppel when Prince Victor of Hohenlohe-Langenburg served under him?


question:
Passage: The Island of Hawaii was first inhabited by Polynesians who arrived in canoes and spread to the other Hawaiian islands. After the contact by the British explorer James Cook the islands became well known and Europeans came and inhabited them. The French government was interested in the islands and wanted to establish Catholicism. The Kingdom of Hawaii became more influenced by the United States which set up trade relations with the Kingdom. After the overthrow of the Hawaiian Kingdom in 1893, the new Republic of Hawaii government lobbied for annexation by the United States. Annexation was approved by President William McKinley and Hawaii was incorporated as part of the territory of the United States on August 12, 1898, and then, in April 1900, organized as the territory of Hawaii.
 Link Information: Cook travelled north and in 1778 became the first European to begin formal contact with the Hawaiian Islands. Answer: 1778
answer:
In what year did James Cook arrive at the Hawaiian Islands?


question:
Passage: Mayer claimed his first victories over United States Army Air Forces (USAAF) four-engine bombers when he shot down two B-17 Flying Fortresses and a B-24 Liberator on 23 November 1942. Together with fellow fighter ace Georg-Peter Eder, Mayer developed the head-on attack as the most effective tactic against the Allied daylight heavy combat box bomber formations. He received the Knight's Cross of the Iron Cross with Oak Leaves on 16 April 1943 after 63 victories. On 1 July 1943, he replaced Walter Oesau as commander of JG 2. He claimed his 90th victory on 31 December 1943 and on 5 February 1944 became the first pilot on the Channel Front to reach 100 victories. Mayer was killed in action on 2 March 1944 while leading an attack on a USAAF bomber formation; he was shot down by P-47 Thunderbolt escort fighters near Montmédy, France. He was posthumously awarded the Knight's Cross of the Iron Cross with Oak Leaves and Swords.
 Link Information: Walter "Gulle" Oesau (28 June 1913 – 11 May 1944) Answer: 30
answer:

How old was the commander Egon Mayer replaced as commander of JG 2?