The ratio of the numbers A and B is 2:7, and their average is 18, then what is the number B?
甲、乙两数的比是2：7，且它们的平均数是18，那么乙数是多少．
<gadget id="calculator">2 + 7</gadget>
<output>9</output>

<gadget id="calculator">2 / 9</gadget>
<output>2/9 = around 0.222222</output>

<gadget id="calculator">18 * (2/9)</gadget>
<output>4</output>

<gadget id="calculator">7 * 4</gadget>
<output>28</output>

<result>28</result>