Dejiang Ceramics Exhibition started on February 20, 2009 and ended on March 7, how many days will the exhibition last?
德江陶瓷器展于2009年2月20日开始，3月7日结束，展期多少天．
<gadget id="calculator">28 - 20</gadget>
<output>8</output>

<gadget id="calculator">8 + 1</gadget>
<output>9</output>

<gadget id="calculator">9 + 7</gadget>
<output>16</output>

<result>16</result>