Dad went on a business trip to attend a meeting, departed on July 16, and returned on August 3, how many days did he spend from departure to return?
爸爸出差参加一个会议，7月16日出发，8月3日返回，他从出发到返回共用了多少天．
<gadget id="calculator">31 - 16</gadget>
<output>15</output>

<gadget id="calculator">15 + 1 + 3</gadget>
<output>19</output>

<result>19</result>