Xiao Ming finished reading a 247-page fairy tale book in 13 days. At this reading speed, how many days would it take Xiao Ming to finish reading a 171-page book?
一本247页的童话书，小明13天就读完，照这样的阅读速度，一本171页的书，小明要多少天读完？
<gadget id="calculator">247 / 13</gadget>
<output>19</output>

<gadget id="calculator">171 / 19</gadget>
<output>9</output>

<result>9</result>