signal soldier rides back and forth between the two camps in the east and the west. The total travel time is 6 hours. The travel time is faster at 30 km per hour, and the return time is slower at 20 km per hour. What is the distance in km between the two camps in the east and west?
一通讯兵骑马往返于东西两个营地之间，共用去时间6小时，去时较快，每小时走30km，回时较慢，每小时走20km，东西两营地之间的距离是多少km？
<gadget id="calculator">2 + 3</gadget>
<output>5</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">6 * (2/5)</gadget>
<output>12/5 = around 2.4</output>

<gadget id="calculator">30 * (12/5)</gadget>
<output>72</output>

<result>72</result>