A train travels from point A to point B. It has traveled the entire distance (3/4), and it is still 100 kilometers away from point B. How long is the railway between AB and AB?
一列火车从A地开往B地，已经行了全程的(3/4)，离B地还有100千米．AB两地之间的铁路长多少千米？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">100 / (1/4)</gadget>
<output>400</output>

<result>400</result>