Add 18 to the denominator of (7/9), how much should the numerator be multiplied to keep the original fraction unchanged.
把(7/9)的分母加上18，要使原分数大小不变，分子应乘以多少．
<gadget id="calculator">9 + 18</gadget>
<output>27</output>

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

<result>3</result>