Add 6 to the former term of 3:7, how much should be added to the latter term to keep the ratio unchanged.
给3：7的前项加上6，要使比值不变，后项应加上多少．
<gadget id="calculator">7 * 3</gadget>
<output>21</output>

<gadget id="calculator">21 - 7</gadget>
<output>14</output>

<result>14</result>