Add 14 to the former term of 7:9, to keep the ratio unchanged, how much should be added to the latter term of the ratio.
把7：9的前项加上14，要使比值不变，比的后项应该加上多少．
<gadget id="calculator">7 + 14</gadget>
<output>21</output>

<gadget id="calculator">21 / 7</gadget>
<output>3</output>

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

<gadget id="calculator">27 - 9</gadget>
<output>18</output>

<result>18</result>