It takes 4 hours for a boat to go back and forth from Pier A to Pier B. When it comes back, it travels 12 kilometers more per hour than when it went. Therefore, the next 2 hours is 18 kilometers longer than the first 2 hours, so how many kilometers is the distance between A and B?
一只船从甲码头到乙码头往返一次共用4小时，回来时顺水比去时每小时多行12千米．因此后2小时比前2小时多行18千米，那么甲、乙两个码头距离是几千米？
<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>