In the Beijing-Hangzhou Grand Canal, the distance between Pier A and Pier B is 180 kilometers. Every day, two passenger ships A and B travel towards each other at the same speed in still water. One day, when departing from Pier A upstream, something falls from the ship. The thing floats on the surface of the water and drifts down the current. After 3 minutes, it is 2 kilometers away from the boat departing from Pier A. How many hours later is it expected that the passenger ship departing from Pier B will encounter this floating thing?
京杭大运河中甲、乙两码头相距180千米，每天定时有A，B两艘客轮以相同的静水速度同时相向而行，某天从上游甲码头出发时船上掉下一件东西，这件东西浮于水面顺流漂下，3分钟后与从甲码头开出的船相距2千米，预计从乙码头出发的客轮几小时后与这件漂浮水面的东西相遇？
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">2 / (1/20)</gadget>
<output>40</output>

<gadget id="calculator">180 / 40</gadget>
<output>9/2 = around 4.5</output>

<result>9/2 = around 4.5</result>