The sum of the numbers A and B is 7.2, the sum of the numbers B and C is 8.4, the sum of the numbers A and C is 8.2, what is the number B?
甲、乙两数的和是7.2，乙、丙两数的和是8.4，甲、丙两数的和是8.2，乙数是多少？
<gadget id="calculator">7.2 + 8.4 + 8.2</gadget>
<output>23.8</output>

<gadget id="calculator">23.8 / 2</gadget>
<output>11.9</output>

<gadget id="calculator">11.9 - 8.2</gadget>
<output>3.7</output>

<result>3.7</result>