Xiaoming traveled with his mother during the summer vacation, starting at 10:00 on July 8, and returning to Hangzhou at 10:00 on July 28. How many days did they travel?
小明暑假里跟着妈妈去旅游，7月8日10时出发，7月28日10时回杭州．他们旅游了几天？
<gadget id="calculator">28 - 8</gadget>
<output>20</output>

<gadget id="calculator">20 + 1</gadget>
<output>21</output>

<result>21</result>