passenger car departs from A to B, and on the way (3/5) the distance is a flat road, then up the mountain and then down the mountain, and finally arrives at B. After staying in place B for 30 minutes, return along the original road. When returning to place A, you find that the bus has traveled a total of 20 kilometers up the mountain. How many kilometers are there between A and B?
一辆客车从甲地出发去乙地，途中(3/5)的路程是平路，然后上山又下山，最终到达乙地．在乙地停留30分钟后沿原路返回，回到甲地时发现客车上山的路程共行20千米．甲乙两地相距多少千米．
<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">20 / (2/5)</gadget>
<output>50</output>

<result>50</result>