The average of the numbers A and B is 42.5. The sum of the numbers A, B and C is 125. What is the number C?
甲、乙两数的平均数是42.5，甲、乙、丙三数之和是125，丙数是多少．
<gadget id="calculator">42.5 * 2</gadget>
<output>85</output>

<gadget id="calculator">125 - 85</gadget>
<output>40</output>

<result>40</result>