A ship sails from port A to port B, and returns immediately after arriving at port B. When going forward, travel 20km per hour, and when returning, travel against the current, travel 6km per hour, and the round trip takes 18 hours. How many kilometers is the distance between A and B ports?
一艘轮船由甲港开往乙港，到达乙港后立即返回．去时顺水，每时行20km，返回时逆水，每时行驶6km，往返共用18时，甲乙两港相距多少千米？
<gadget id="calculator">18 * 6</gadget>
<output>108</output>

<gadget id="calculator">20 + 6</gadget>
<output>26</output>

<gadget id="calculator">108 / 26</gadget>
<output>54/13 = around 4.153846</output>

<gadget id="calculator">20 * (54/13)</gadget>
<output>1_080/13 = around 83.076923</output>

<result>1_080/13 = around 83.076923</result>