Expand the former term of 5:12 to 3 times of the original one, how much should be added to the latter term to keep the ratio unchanged.
将5：12的前项扩大到原来的3倍，要使比值不变，后项应加多少．
<gadget id="calculator">36 - 12</gadget>
<output>24</output>

<result>24</result>