A ratio, the ratio of front and back items is 3:5, if 6 is added to the former item, how much should be added to the latter item to keep the ratio unchanged.
一个比，前后项的比是3：5，如果前项加上6，要使比值不变，后项应加上多少．
<gadget id="calculator">15 - 5</gadget>
<output>10</output>

<result>10</result>