Two students, A and B, go to the county seat from school. A travels 4 kilometers per hour, and B travels 6 kilometers per hour. A starts 50 minutes first, but B arrives 20 minutes later than A. Find the distance between the two places.
甲、乙两名同学从学校去县城，甲每小时行4千米，乙每小时行6千米，甲先出发50分钟，结果乙比甲晚到20分，求两地之间的距离．
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(1/4) - (1/6)</gadget>
<output>1/12 = around 0.083333</output>

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

<result>6</result>