In 3:5, if the former term is multiplied by 3, to keep the ratio unchanged, how much should be added to the latter term.
在3：5里，如果前项乘以3，要使比值不变，后项应加上多少．
<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<gadget id="calculator">15 - 5</gadget>
<output>10</output>

<result>10</result>