If the average of the three numbers A, B, and C is 42, and the average of the two numbers B and C is 43, what is the number of A?
甲、乙、丙三个数的平均数是42，乙、丙两个数的平均数是43，则甲数是多少．
<gadget id="calculator">42 * 3</gadget>
<output>126</output>

<gadget id="calculator">43 * 2</gadget>
<output>86</output>

<gadget id="calculator">126 - 86</gadget>
<output>40</output>

<result>40</result>