The former term of 3:5 is increased to 12, how much should the latter term be multiplied to keep the ratio constant.
3：5的前项增加到12，要使比值不变，后项要乘以多少．
<gadget id="calculator">3 + 12</gadget>
<output>15</output>

<gadget id="calculator">15 / 3</gadget>
<output>5</output>

<result>5</result>