What is the difference between 21.51 minus 3.51 plus 6.8?
21.51减去3.51加上6.8的和，差是多少？
<gadget id="calculator">3.51 + 6.8</gadget>
<output>10.31</output>

<gadget id="calculator">21.51 - 10.31</gadget>
<output>11.2</output>

<result>11.2</result>