Teacher: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.
Teacher: Now, understand the problem? Solve this instance: Passage: Anaukpetlun then brought trans-Salween Shan states under his rule in the 1620s. In February 1622, his forces took Kengtung, which had been held by an ally of Lan Xang, after a fierce battle. Reinforced Burmese armies led by the king's brothers Thalun and Minye Kyawswa II invaded the Chinese Shan states in present-day southern Yunnan in May 1622. For the next 20 months, Burmese forces chased Kenghung troops. Finally in January 1624, Kenghung and Kengyun both surrendered. Kengyun promptly rebelled the following year but it was put down in December 1626 by the king's brothers. By then, Nyaungyan and Anaukpetlun had restored much of Bayinnaung's empire. Only Siam and Lan Xang remained outside the Restored Toungoo Empire. But the Burmese would not overstretch again. They would not launch major invasions against these neighbours until the 1760s.
Question: Thalun and Minye Kyawswa II invaded the Chinese Shan states how many years before they surrendered?
Answer type: Number
Student:
2.