This task involves annotating the answer type to a given question that involve some kind of complex reasoning (including numerical reasoning). Note that the questions require looking at more than one part of the passage to answer. There are 3 possible answer types (i) spans, (ii) numbers and (iii) dates. If the answer can be found in the passage, label it as "span". If the answer is a number, label as "number". Similarly, label "date" if you think the answer to the given question is a date.
Q: Passage: The first recorded contact between Thailand and the United States came in 1818, when an American ship captain visited the country, bearing a letter from U.S. President James Monroe. Chang and Eng Bunker immigrated in the early 1830s. In 1832, President Andrew Jackson sent his envoy Edmund Roberts in the U.S. sloop-of-war Peacock, to the courts of Cochin-China, Siam and Muscat. Roberts concluded a Treaty of Amity and Commerce on March 20, 1833, with the Chao-Phraya Phra Klang representing King Phra Nang Klao; ratifications exchanged April 14, 1836; proclaimed June 24, 1837. Naval surgeon William Ruschenberger accompanied the return mission for exchange of ratifications. His account and that of Mr. Roberts were collected, edited and re-published as Two Yankee Diplomats In 1830's Siam. The 150th anniversary of Roberts' mission was marked by in 1982 by issuance of the first edition of The Eagle and the Elephant: Thai-American relations since 1833, followed by multiple re-issues including a 1987 royal celebration edition and a 1997 golden jubilee edition. This was affirmed by former prime minister Samak Sundaravej, who in 2008, met George W. Bush on the "occasion of the celebration of 175th anniversary of Thai-American relations." Thailand is thus the first Asian nation to have a formal diplomatic agreement with the United States; eleven years before the Great Qing and twenty-one years before Tokugawa Japan. In May 1856, Townsend Harris, a representative of President Franklin Pierce, negotiated a modified Treaty of Amity, Commerce, and Navigation with representatives of King Mongkut that granted Americans additional extraterritorial rights. Stephen Mattoon, an American missionary who acted as Harris's translator, was appointed the first United States consul to Siam.
Question: When was the 175th anniversary of Thai-American relations?
A:
date