There were originally 10 people in the bookstore, 7 people just came in, and 9 people went out, how many people are there now?
书店原有10个人，刚进来了7个人，又走出去9个人，现在有多少人？
<gadget id="calculator">7 - 9</gadget>
<output>-2</output>

<gadget id="calculator">10 + (-2)</gadget>
<output>8</output>

<result>8</result>