The young pioneers participated in the 2006 summer camp. They set off on July 18 and came back on August 8. How many days has the summer camp been held?
少先队员参加2006年夏令营活动，他们7月18日出发，8月8日回来．夏令营举办了多少天天．
<gadget id="calculator">31 - 18</gadget>
<output>13</output>

<gadget id="calculator">8 - 1</gadget>
<output>7</output>

<gadget id="calculator">13 + 7</gadget>
<output>20</output>

<result>20</result>