The average of the three numbers A, B, and C is 13.5, and the average of the two numbers B and C is 14.2. What is the number of A?
甲、乙、丙三个数的平均数是13.5，乙、丙两个数的平均数是14.2，甲数是多少？
<gadget id="calculator">13.5 * 3</gadget>
<output>40.5</output>

<gadget id="calculator">14.2 * 2</gadget>
<output>28.4</output>

<gadget id="calculator">40.5 - 28.4</gadget>
<output>12.1</output>

<result>12.1</result>