Detailed Instructions: This task involves creating answers to complex questions, from a given passage. Answering these questions, typically involve understanding multiple sentences. Make sure that your answer has the same type as the "answer type" mentioned in input. The provided "answer type" can be of any of the following types: "span", "date", "number". A "span" answer is a continuous phrase taken directly from the passage or question. You can directly copy-paste the text from the passage or the question for span type answers. If you find multiple spans, please add them all as a comma separated list. Please restrict each span to five words. A "number" type answer can include a digit specifying an actual value. For "date" type answers, use DD MM YYYY format e.g. 11 Jan 1992. If full date is not available in the passage you can write partial date such as 1992 or Jan 1992. If you find multiple spans, please add them all as a comma separated list. Please restrict each span to five words.
Q: Passage: The National Labor Union , founded in 1866, was the first national labor federation in the United States. It was dissolved in 1872. The regional Order of the Knights of St. Crispin was founded in the northeast in 1867 and claimed 50,000 members by 1870, by far the largest union in the country. A closely associated union of women, the Daughters of St. Crispin, formed in 1870. In 1879 the Knights formally admitted women, who by 1886 comprised 10% of the union's membership, but it was poorly organized and soon declined. They fought encroachments of machinery and unskilled labor on autonomy of skilled shoe workers. One provision in the Crispin constitution explicitly sought to limit the entry of "green hands" into the trade, but this failed because the new machines could be operated by semi-skilled workers and produce more shoes than hand sewing.
Question: How many years did the National Labor Union operate for until it was dissolved?
Answer type: Number
A:
6.