The average of the three numbers A, B, and C is 9, the average of A and B is 7, and the sum of B and C is 18. What is the number of B?
甲、乙、丙三个数的平均数是9，甲、乙平均数为7，乙、丙之和为18，乙数是多少．
<gadget id="calculator">7 * 2</gadget>
<output>14</output>

<gadget id="calculator">14 + 18</gadget>
<output>32</output>

<gadget id="calculator">9 * 3</gadget>
<output>27</output>

<gadget id="calculator">32 - 27</gadget>
<output>5</output>

<result>5</result>