What is the difference between the sum of 16.7 and 12.2 minus 20?
16.7与12.2的和减去20，差是多少？
<gadget id="calculator">16.7 + 12.2</gadget>
<output>28.9</output>

<gadget id="calculator">28.9 - 20</gadget>
<output>8.9</output>

<result>8.9</result>