Knowing that the numerator of (3/7) becomes 21, what should the denominator be to keep the size of the fraction constant?
已知(3/7)的分子变成了21，要使分数的大小不变，那么分母应为多少
<gadget id="calculator">21 / 3</gadget>
<output>7</output>

<gadget id="calculator">7 * 7</gadget>
<output>49</output>

<result>49</result>