Expand the former term of 8:15 to 3 times of the original, how much should the latter term be increased to keep the ratio unchanged.
把8：15的前项扩大到原来的3倍，要使比值不变，后项应增加多少．
<gadget id="calculator">45 - 15</gadget>
<output>30</output>

<result>30</result>