If 5 is added to the former term of 5:12, to keep the ratio unchanged, how much should be added to the latter term
如果5：12的前项加上5，要使比值不变，则后项应加上多少
<gadget id="calculator">12 * 2</gadget>
<output>24</output>

<gadget id="calculator">24 - 12</gadget>
<output>12</output>

<result>12</result>