There are two upper and lower ports 45 kilometers apart on a certain river. Every day, passenger ships A and B with the same speed depart from the two ports at the same time and go towards each other. On this day, ship A drops an object from the upper port, and the object floats on the water. Float down the current, and after 4 minutes, the distance from ship A is 1 kilometer. It is expected that ship B will meet this object a few hours after departure.
某河有相距45千米的上下两港，每天定时有甲乙两船速相同的客轮分别从两港同时出发相向而行，这天甲船从上港出发掉下一物，此物浮于水面顺水漂下，4分钟后与甲船相距1千米，预计乙船出发后几小时可与此物相遇．
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">1 / (1/15)</gadget>
<output>15</output>

<gadget id="calculator">45 / 15</gadget>
<output>3</output>

<result>3</result>