If the scale of a picture is 1:300000 and the distance on the picture is 4 cm, what is the actual distance in kilometers?
如果一幅图的比例尺为1：300000，图上距离为4厘米，那么实际距离是多少千米．
<gadget id="calculator">1 / 300_000</gadget>
<output>1/300_000 = around 0.000003</output>

<gadget id="calculator">4 / (1/300_000) / 100_000</gadget>
<output>12</output>

<result>12</result>