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: Kublai essentially demanded that Japan become a vassal and send tribute under a threat of conflict. However, the emissaries returned empty-handed. A second set of emissaries were sent in 1268, returning empty-handed like the first. Both sets of emissaries met with the Chinzei Bugyo, or Defense Commissioner for the West, who passed on the message to Shikken, Hojo Tokimune, Japan's ruler in Kamakura and to the Emperor of Japan in Kyoto. After discussing the letters with his inner circle, there was much debate, but the Shikken had his mind made up; he had the emissaries sent back with no answer. The Mongols continued to send demands, some through Korean emissaries and some through Mongol ambassadors on March 7, 1269; September 17, 1269; September 1271; and May 1272. However, each time, the bearers were not permitted to land in Kyushu. The Imperial Court suggested compromise, but really had little effect in the matter, due to political marginalization after the Jokyu War. The uncompromising shogunate ordered all those who held fiefs in Kyushu, the area closest to the Korean Peninsula and thus most likely to be attacked, to return to their lands and forces in Kyushu moved west, further securing the most likely landing points. After acknowledging its importance, the Imperial Court led great prayer services, and much government business was put off to deal with this crisis.
How many days did the Mongols send demands through Korean emissaries and some Mongol ambassadors?