The average weight of A, B, and C is 39 kg. The sum of the weight of A and B is 75 kg. What is the weight of C in kg?
甲、乙、丙三人的平均体重是39千克，甲乙两人的重量和是75千克，丙的体重是多少千克．
<gadget id="calculator">39 * 3</gadget>
<output>117</output>

<gadget id="calculator">117 - 75</gadget>
<output>42</output>

<result>42</result>