Detailed Instructions: 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.
Problem:Passage: On April 17, 13 ships arrived at Tokunoshima and dispersed. Two ships arrived at Kanaguma, but nothing happened. Eight ships arrived at Wanya. The ships were besieged all night by 1,000 people. On April 18, Satsuma troops disembarked, fired into the crowds, and killed 50 people. Three ships arrived at Akitoku, and were attacked at the water's edge by the Akitoku people. However, troops quickly fought back and killed 20-30 people. The Satsuma fleet also arrived at Akitoku at 4pm, April 20. On April 21, Kabayama left for Okierabu Island with 10 ships in advance. Others left Tokunoshima at 10am, April 24, and arrived at Okierabu at sunset. They met Kabayama and his ships there, and quickly departed for Ryukyu Island.
Question: When did Kabayama leave to Ryukyu Island?
Solution:
date