In 8:12, if 2 is added to the former term, how much should be added to the latter term to keep the ratio unchanged.
在8：12中，如果前项加上2，要使比值不变，后项应加上多少．
<gadget id="calculator">12 * 1.25</gadget>
<output>15</output>

<gadget id="calculator">15 - 12</gadget>
<output>3</output>

<result>3</result>