Add 10 to the former term of 4:12, in order to keep the obtained ratio unchanged, how much should be added to the latter term of the ratio.
把4：12的前项加上10，为了要使所得的比值不变，比的后项应加上多少．
<gadget id="calculator">42 - 12</gadget>
<output>30</output>

<result>30</result>