In the ratio 0.3:0.4=9:12, if you add 0.6 to the second item, the ratio is still valid, then how much should the fourth item be multiplied by.
在比例0.3：0.4=9：12中，如果给第二项加上0.6，比例仍然成立，那么第四项应该乘以多少．
<gadget id="calculator">0.4 + 0.6</gadget>
<output>1</output>

<gadget id="calculator">9 / 0.3 / 1 / 12</gadget>
<output>2.5</output>

<result>2.5</result>