In the ratio 5:30=12:72, if 5 is added to 15, how much should be added to 12 to make the ratio still valid.
在比例5：30=12：72中，如果5加上15，要使比例依然成立，12应加上多少．
<gadget id="calculator">20 * 72</gadget>
<output>1_440</output>

<gadget id="calculator">1_440 / 30</gadget>
<output>48</output>

<gadget id="calculator">48 - 12</gadget>
<output>36</output>

<result>36</result>