What is the difference between 30.6 minus the sum of 12.1 and 8.7?
30.6减去12.1与8.7的和，差是多少？
<gadget id="calculator">12.1 + 8.7</gadget>
<output>20.8</output>

<gadget id="calculator">30.6 - 20.8</gadget>
<output>9.8</output>

<result>9.8</result>