Increase the numerator of (2/7) by 8, how much should the denominator be increased to keep the size of the fraction constant.
把(2/7)的分子增加8，要使分数的大小不变，分母应该增加多少．
<gadget id="calculator">2 + 8</gadget>
<output>10</output>

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<gadget id="calculator">7 * 5</gadget>
<output>35</output>

<gadget id="calculator">35 - 7</gadget>
<output>28</output>

<result>28</result>