The fuel carried by a ship can be used for up to 18 hours. When it sails out, it travels 30 kilometers per hour along the current. When it returns, it travels against the current. The distance traveled per hour is along the current (4/5), so how much does the ship travel after departure? Kilometers should return immediately?
一艘轮船所带的燃料最多可用18小时，驶出时顺水，每小时行驶30千米，返回时逆水，每小时行的路程是顺水的(4/5)，那么这艘轮船出发后行驶多少千米就应立即返回？
<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">30 * (4/5)</gadget>
<output>24</output>

<gadget id="calculator">1 / 24</gadget>
<output>1/24 = around 0.041667</output>

<gadget id="calculator">(1/30) + (1/24)</gadget>
<output>3/40 = around 0.075</output>

<gadget id="calculator">18 / (3/40)</gadget>
<output>240</output>

<result>240</result>