In 3:4, the former term of the ratio is multiplied by 5, to keep the ratio unchanged, how much should be added to the latter term of the ratio
在3：4中，比的前项乘以5，要使比值不变，比的后项应加上多少
<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<gadget id="calculator">20 - 4</gadget>
<output>16</output>

<result>16</result>