In the ratio of 35:10=21:6, if the latter term of the first ratio is increased by 30, how much should be added to the latter term of the second ratio to make the ratio valid.
在比例35：10=21：6中，如果将第一个比的后项增加30，第二个比的后项应该加上多少才能使比例成立．
<gadget id="calculator">40 * 21</gadget>
<output>840</output>

<gadget id="calculator">840 / 35</gadget>
<output>24</output>

<gadget id="calculator">24 - 6</gadget>
<output>18</output>

<result>18</result>