In the ratio 12:45=8:30, if the latter term of the first ratio is increased by 15, then how much should the former term of the second ratio be to make the ratio valid.
在比例12：45=8：30中，如果第一个比的后项增加15，那么第二个比的前项应该多少才能使比例成立．
<gadget id="calculator">45 + 15</gadget>
<output>60</output>

<gadget id="calculator">30 / 60</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">12 * (1/2)</gadget>
<output>6</output>

<gadget id="calculator">8 - 6</gadget>
<output>2</output>

<result>2</result>