Given the task definition and input, reply with output. This task involves creating questions from a given passage that involve some kind of complex reasoning (including numerical reasoning).
The generated questions must require looking at more than one part of the passage to answer. Try to use a variety of reasoning types in your questions (some of the sample reasoning types are illustrated in the 'positive examples' field) and also have a variety of answer types (spans, numbers, dates). A span is a continuous phrase taken directly from the passage or question. In such questions, the answer spans are recommended to be five words. Questions with answer type "number", are expected to start with "How many". For instance, "How long did an event last?" can be phrased as "How many years did an event last?". To increase diversity, try to create more questions for which the answer will be multiple spans. Please create questions that require AT LEAST 2 arithmetic operations as illustrated in the 'positive examples' field. You are encouraged to try DIFFERENT COMBINATIONS of operations and not just limit to the combinations shown in those examples. The more challenging questions you create, the better it is.

Passage: Direct U.S. military involvement ended on 15 August 1973 as a result of the Case-Church Amendment passed by the U.S. Congress. The fall of Saigon by the North Vietnamese Army in April 1975 marked the end of the war, and North and South Vietnam were reunified the following year. The war exacted a huge human cost in terms of fatalities (see Vietnam War casualties). Estimates of the number of Vietnamese soldiers and civilians killed vary from 966,000 to 3.8 million. Some 275,000-310,000 Khmer people, 20,000-62,000 Lao people, and 58,220 U.S. service members also died in the conflict, and a further 1,626 remain missing in action. The Sino-Soviet split re-emerged following the lull during the Vietnam War and ties between the DRV and its Cambodian allies in the GRUNK, the newly-formed Democratic Kampuchea begun almost immediately in a series of border raids by the Khmer Rouge and erupted into the Cambodian-Vietnamese War, with Peoples Liberation Army directly intervening in the Sino-Vietnamese War. The end of the war and resumption of the Third Indochina War would precipitate the Vietnamese boat people and the bigger Indochina refugee crisis, which saw an estimated 250,000 people perish at sea.
How many years after U.S. military involvement ended did the Vietnam War end?