Add 8 to the former term of 4:15, how much should the latter term be multiplied to keep the ratio unchanged.
将4：15的前项增加8，要使比值不变，后项应乘多少．
<gadget id="calculator">4 + 8</gadget>
<output>12</output>

<gadget id="calculator">12 / 4</gadget>
<output>3</output>

<result>3</result>