The average of the three numbers A, B, and C is 42, and the numbers B and C are 45 and 40 respectively, so what is the number of A?
甲、乙、丙三个数的平均数是42，乙、丙两数分别是45、40，那么甲数是多少．
<gadget id="calculator">42 * 3</gadget>
<output>126</output>

<gadget id="calculator">126 - 45 - 40</gadget>
<output>41</output>

<result>41</result>