The average of the two numbers A and B is 17, and the average of the two numbers B and C is 20, so how much more C is than A.
A、B两数的平均数是17，B、C两数的平均数是20，那么C比A多多少．
<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">17 * 2</gadget>
<output>34</output>

<gadget id="calculator">40 - 34</gadget>
<output>6</output>

<result>6</result>