It takes 4 hours for a ship to go back and forth from Pier A to Pier B. If you go with the current, you will travel 10 kilometers per hour against the current than when you return, so you will travel 18 kilometers more in the first 2 hours than in the last 2 hours. Find the distance between the two piers A and B.
一艘轮船，从甲码头到乙码头往返共用去4小时．去时顺水，这样就比返回时逆水每小时多行10千米，因此前2小时比后2小时多行18千米．求甲乙两码头间的距离．
<gadget id="calculator">18 / 12</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">4 - (3/2)</gadget>
<output>5/2 = around 2.5</output>

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

<gadget id="calculator">18 / 1</gadget>
<output>18</output>

<gadget id="calculator">18 * (5/2)</gadget>
<output>45</output>

<result>45</result>